The Parnells of Avondale were descended from a Protestant English merchant family, which came to prominence in Congleton, Cheshire, early in the 17th century where as Baron Congleton two generations held the office of Mayor of Congleton before moving to Ireland. The family produced a number of notable figures, including Thomas Parnell (1679–1718), the Irish poet, and Henry Parnell, 1st Baron Congleton (1776–1842), the Irish Politician. Parnell's grandfather william Parnell (1780–1821), who inherited the Avondale Estate in 1795, was a liberal Irish MP for Wicklow from 1817–1820. Thus, from birth, Charles Stewart Parnell possessed an extraordinary number of links to many elements of society; he was linked to the old Irish Parliamentary tradition via his great-grandfather and grandfather, to the American War of Independence via his grandfather, to the War of 1812 (where his grandfather had been awarded a gold medal by the United States Congress for gallantry). Parnell belonged to the Church of Ireland, disestablished in 1871 (its members mostly unionists) though in later years he began to drop away from formal church attendance; and he was connected with the aristocracy through the Powerscourts. Yet it was as a leader of Irish Nationalism that Parnell established his fame.

Charles Stewart Parnell was born in County Wicklow, the third son and seventh child of John Henry Parnell (1811–1859), a wealthy Anglo-Irish landowner, and his American wife Delia Tudor Stewart (1816–1898) of Bordentown, New Jersey, daughter of the American naval hero, Admiral Charles Stewart (the stepson of one of George Washington's bodyguards). There were eleven children in all: five boys and six girls. Admiral Stewart's mother, Parnell's great-grandmother, belonged to the Tudor family, so Parnell had a distant relationship with the British Royal Family. John Henry Parnell himself was a cousin of one of Ireland's leading aristocrats, Viscount Powerscourt, and also the grandson of a Chancellor of the Exchequer in Grattan's Parliament, Sir John Parnell, who lost office in 1799 when he opposed the Act of Union.

Parnell's parents separated when he was six, and as a boy he was sent to different schools in England, where he spent an unhappy youth. His father died in 1859 and he inherited the Avondale estate, while his older brother John inherited another estate in Armagh. The young Parnell studied at Magdalene College, Cambridge (1865–69) but, due to the troubled financial circumstances of the estate he inherited, he was absent a great deal and never completed his degree. In 1871, he joined his elder brother John Howard Parnell (1843–1923), who farmed in Alabama (later an Irish Parnellite MP and heir to the Avondale estate), on an extended tour of the United States. Their travels took them mostly through the South and apparently the brothers neither spent much time in centres of Irish immigration nor sought out Irish-Americans.

Parliament was dissolved and elections called, with Irish Home Rule the central issue. Gladstone hoped to repeat his triumph of 1868, when he fought and won a General Election to obtain a mandate for Irish Disestablishment (which had been a major cause of dispute between Conservatives and Liberals since the 1830s), but the result of the July 1886 general election was Liberal defeat. The Conservatives and the Liberal Unionist Party returned with a majority of 118 over the combined Gladstonian Liberals and Parnell's 85 Irish Party seats. Salisbury formed his second government – a minority Conservative government with Liberal Unionist support.

In 1874, he became High Sheriff of Wicklow, his home county in which he was also an officer in the Wicklow militia. He was noted as an improving landowner who played an important part in opening the south Wicklow area to industrialisation. His attention was drawn to the theme dominating the Irish political scene of the mid-1870s, Isaac Butt's Home Rule League formed in 1873 to campaign for a moderate degree of self-government. It was in support of this movement that Parnell first tried to stand for election in Wicklow, but as high sheriff was disqualified. He failed again in 1874 as home rule candidate in a County Dublin by-election.

Parnell was first elected to the House of Commons as a Home Rule League Member of Parliament (MP) for County Meath on 21 April 1875 in a by-election backed by Fenian Patrick Egan. He replaced the deceased League MP, veteran Young Irelander John Martin. He subsequently sat for the constituency of Youghal, Cork from 1880 until 1891.

During his first year Parnell remained a reserved observer of parliamentary proceedings. He first came to attention in the public eye when in 1876 he claimed in the Commons that he did not believe that any murder had been committed by Fenians in Manchester. This drew the interest of the Irish Republican Brotherhood (IRB), a physical force Irish organisation that had staged a rebellion in 1867. Parnell made it his Business to cultivate Fenian sentiments both in Britain and Ireland and became associated with the more radical wing of the Home Rule League, which included Joseph Biggar (MP for Cavan from 1874), John O'Connor Power (MP for County Mayo from 1874) (both, although constitutionalists, had links with the IRB), Edmund Dwyer-Gray (MP for Tipperary from 1877), and Frank Hugh O'Donnell (MP for Dungarvan from 1877). He engaged with them and played a leading role in a policy of obstructionism (i.e., the use of technical procedures to disrupt the House of Commons' ability to function) to force the House to pay more attention to Irish issues, which had previously been ignored. Obstruction involved giving lengthy speeches which were largely irrelevant to the topic at hand. This behaviour was opposed by the less aggressive chairman (leader) of the Home Rule League, Isaac Butt.

From August 1877 Parnell held a number of private meetings with prominent Fenian Leaders. He visited Paris where he met John O'Leary and J. J. O'Kelly both of whom were impressed by him and reported positively to the most capable and militant Leader of the American republican Clan na Gael organisation, John Devoy. In December at a reception for Michael Davitt on his release from prison, he met william Carrol who assured him of Clan na Gael's support in the struggle for Irish self-government. This led to a meeting in March 1878 between influential constitutionalists, Parnell and Frank Hugh O'Donnell, and leading Fenians O'Kelly, O'Leary and Carroll. This was followed by a telegram from John Devoy in October 1878 which offered Parnell a "New Departure" deal of separating militancy from the constitutional movement as a path to all-Ireland self-government, under certain conditions: abandonment of a federal solution in favour of separatist self-government, vigorous agitation in the land question on the basis of peasant proprietorship, exclusion of all sectarian issues, collective voting by party members and energetic resistance to coercive legislation.

Although the League discouraged violence, agrarian outrages grew from 863 incidents in 1879 to 2,590 in 1880 after evictions increased from 1,238 to 2,110 in the same period. Parnell saw the need to replace violent agitation with country-wide mass meetings and the application of Davitt's boycott, also as a means of achieving his objective of self-government. Gladstone was alarmed at the power of the Land League at the end of 1880. He attempted to defuse the land question with dual ownership in the Second Land Act of 1881, establishing a Land Commission that reduced rents and enabled some tenants to buy their farms. These halted arbitrary evictions, but not where rent was unpaid.

Charles Stewart Parnell possessed the remarkable attribute of charisma, was an enigmatic personality and politically gifted, and is regarded as one of the most extraordinary figures in Irish and British politics. He played a part in the process that undermined his own Anglo-Irish caste; within two decades absentee landlords were almost unknown in Ireland. He created single-handedly in the Irish Party Britain's first modern, disciplined, political-party machine. He held all the reins of Irish nationalism and also harnessed Irish-America to Finance the cause. He played an important role in the rise and fall of British governments in the mid-1880s and in Gladstone's conversion to Irish Home Rule.

Over a century after his death he is still surrounded by public interest. His death, and the divorce upheaval which preceded it, gave him a public appeal and interest that other contemporaries, such as Timothy Healy or John Dillon, could not match. His leading biographer, F. S. L. Lyons, says historians emphasize numerous major achievements: Above all there is the emphasis on constitutional action, as historians point to the Land Act of 1881; The creation of the powerful third force in Parliament using a highly disciplined party that he controlled; including Ireland in the Reform Act of 1884, while preventing any reduction in the number of Irish seats; the powerful role of the Irish National League and organizing locally, especially County conventions that taught peasants about democratic self-government; forcing Home Rule to be a central issue in British politics; and persuading the great majority of the Liberal party to adopt his cause. Lyons agrees that these were remarkable achievements, but emphasizes that Parnell did not accomplish them alone, but only in close coordination with men such as Gladstone and Davitt.

Parnell next became the centre of public attention when in March and April 1887 he found himself accused by the British newspaper The Times of supporting the brutal murders in May 1882 of the newly appointed Chief Secretary for Ireland, Lord Frederick Cavendish, and the Permanent Under-Secretary, Thomas Henry Burke, in Dublin's Phoenix Park, and of the general involvement of his movement with crime (i.e., with illegal organisations such as the IRB). Letters were published which suggested Parnell was complicit in the murders. The most important one, dated 15 May 1882, ran as follows:

Both British parties toyed with various suggestions for greater self-government for Ireland. In March 1885 the Cabinet rejected the proposal of radical minister Joseph Chamberlain of democratic county councils which in turn would elect a Central Board for Ireland. Gladstone on the other hand saying he was prepared to go 'rather further' than the idea of a Central Board . After Gladstone's government fell in June 1885, Parnell urged the Irish voters in Britain to vote against the Liberals. The November general elections (delayed because boundaries were being redrawn and new registers prepared after the Third Reform Act) brought about a hung Parliament in which the Liberals with 335 seats won 86 more than the Conservatives, with a Parnellite bloc of 86 Irish Home Rule MPs holding the balance of power in the Commons. Parnell's task was now to win acceptance of the principle of a Dublin parliament.

Parnell's leadership was first put to the test in February 1886 when he forced the candidature of Captain william O'Shea, who had negotiated the Kilmainham Treaty, for a Galway by-election. Parnell rode roughshod over his lieutenants Healy, Dillon and O'Brien who were not in favour of O'Shea. Galway was the harbinger of the fatal crisis to come. O'Shea had already separated from his wife Katharine O'Shea, but would not divorce her as she was expecting a substantial inheritance. Mrs. O'Shea acted as liaison in 1885 with Gladstone during proposals for the First Home Rule Bill. Parnell later took up residence with her in Eltham, Kent in the summer of 1886, and was a known overnight visitor at the O'Shea house in Brockley, London. When Mrs O'Shea's aunt died in 1889, her money was left in trust.

Parnell's personal complexities or his perception of a need for political expediency to his goal permitted him to condone radical republican and the atheist Charles Bradlaugh, while he associated himself with the hierarchy of the Catholic Church. Parnell was a close friend and political associate of fellow land reform Activist Thomas Nulty, the Roman Catholic Bishop of Meath, until Parnell's divorce crisis in 1889. Charles Parnell was linked both with the landed aristocracy class and the Irish Republican Brotherhood, with speculation in the 1890s that he may have even joined the latter organisation. The Historian Andrew Roberts argues that he was sworn into the IRB in the Old Library at Trinity College Dublin in May 1882 and that this was concealed for 40 years. In Barry O'Brien's Parnell, X, Fenian Parliamentarian John O'Connor Power, relates, 'And, in fact, I was, about this time [1877], deputed to ask Parnell to join us. I did ask him. He said "No" without a moment's hesitation.' He was conservative by nature, leading some historians to suggest that personally he would have been closer to the Conservative rather than to the Liberal Party, but for political needs. Andrew Kettle, Parnell's right-hand man, who shared a lot of his opinions, wrote of his own views, "I confess that I felt [in 1885], and still feel, a greater leaning towards the British Tory party than I ever could have towards the so-called Liberals." In later years, the double effect of the Phoenix Park trauma and the O'Shea affair reinforced the conservative side of his nature.

Parnell was played by a clean-shaven Clark Gable in Parnell, the 1937 MGM production about the Irish leader. The film is notable as being Gable's biggest flop and occurred at the height of his career, when almost every Gable film was a smash hit. Parnell was portrayed by Robert Donat in the 1947 film Captain Boycott. In 1954, Patrick McGoohan played Parnell in "The Fall of Parnell (December 6, 1890)", an episode of the historical television series You Are There.

He is also commemorated on the first Sunday after the anniversary of his death on 6 October, known as Ivy Day,which originated when the mourners at his funeral in 1891, taking their cue from a wreath of ivy sent by a Cork woman "as the best offering she could afford," took ivy leaves from the walls and stuck them in their lapels. Ever after, the ivy leaf became the Parnellite emblem, worn by his followers when they gathered to honour their lost leader.

In Knut Hamsun's 1892 novel Mysteries, the characters, on a couple of occasions, briefly discuss Charles Stewart Parnell, particularly in relation to Gladstone: "Dr. Stenerson had a high opinion of Parnell, but if Gladstone was so opposed to him, he must know what he was about—with apologies to the host, Mr. Nagel, who couldn't forgive Gladstone for being an honourable man". Parnell's death shocks the character Eleanor in Virginia Woolf's novel The Years, published in 1937: "...how could he be dead? It was like something fading in the sky."

The Liberal split made the Unionists (the Liberal Unionists sat in coalition with the Conservatives after 1895 and would eventually merge with them) the dominant force in British politics until 1906, with strong support in Lancashire, Liverpool & Manchester, Birmingham (the fiefdom of its former mayor Joseph Chamberlain who as recently as 1885 had been a furious enemy of the Conservatives) and the House of Lords where many Whigs sat (a second Home Rule Bill would pass the Commons in 1893 only to be overwhelmingly defeated in the Lords).

His brother John Howard inherited the Avondale estate. He found it heavily mortgaged and eventually sold it in 1899. Five years later, at the suggestion of Horace Plunkett it was purchased by the state. It is open to public view and is where the "Parnell Society" holds its annual August summer school. The "Parnell National Memorial Park" is in nearby Rathdrum, County Wicklow. Dublin has locations named Parnell Street and Parnell Square. At the north end of O'Connell Street stands the Parnell Monument. This was planned and organised by John Redmond, who chose the American Augustus Saint Gaudens to sculpt the statue; it was funded by Americans and completed in 1911. Art critics said it was not an artistic success.

When the annual party leadership election was held on 25 November, Gladstone's threat was not conveyed to the members until after they had loyally re-elected their 'chief' in his office. Gladstone published his warning in a letter the next day; subsequently, angry members demanded a new meeting, and this was called for 1 December. Parnell issued a manifesto on 29 November saying a section of the party had lost its independence; he falsified Gladstone's terms for Home Rule and said they were inadequate. A total of 73 members were present for the fateful meeting in committee room 15 at Westminster. Leaders tried desperately to achieve a compromise in which Parnell would temporarily withdraw. Parnell refused. He vehemently insisted that the independence of the Irish party could not be compromised either by Gladstone or by the Catholic hierarchy. As chairman, he blocked any motion to remove him. On 6 December, after five days of vehement debate, a majority of 44 present led by Justin McCarthy walked out to found a new organisation, thus creating rival Parnellite and anti-Parnellite parties. The minority of 28 who remained true to their embattled 'Chief' continued in the Irish National League under John Redmond. However, all of his former close associates, Michael Davitt, John Dillon, william O'Brien and Timothy Healy deserted him to join the anti-Parnellites. The vast majority of anti-Parnellites formed the Irish National Federation, later led by John Dillon and supported by the Catholic Church. The bitterness of the split tore Ireland apart and resonated well into the next century. Parnell soon died, and his faction dissipated. The majority faction henceforth played only a minor role in British or Irish politics until the next time the UK had a hung Parliament, in 1910.

Parnell next turned to the Home Rule League Party, of which he was to remain the re-elected leader for over a decade, spending most of his time at Westminster, with Henry Campbell as his personal secretary. He fundamentally changed the party, replicated the INL structure within it and created a well-organised grass roots structure, introduced membership to replace "ad hoc" informal groupings in which MPs with little commitment to the party voted differently on issues, often against their own party. Or they simply did not attend the House of Commons at all (some citing expense, given that MPs were unpaid until 1911 and the journey to Westminster both costly and arduous).

Parnell is the subject of a discussion in Irish author James Joyce's first chapter of the semi-autobiographical novel A Portrait of the Artist as a Young Man, first serialised in The Egoist magazine in 1914–15. Parnell appears in several stories in Dubliners, notably in "Ivy Day in the Committee Room". He is also discussed in Ulysses, as is his brother. The main character in Finnegans Wake, HCE, is partially based on Parnell; among other resemblances, both are accused of transgressions in Phoenix Park.

Parnell is toasted in the famous 1938 poem of william Butler Yeats, "Come Gather Round Me, Parnellites", while he is also referred to in "To a Shade", where he performs the famous "C.S.Parnell Style", and in Yeats' two-line poem "Parnell".

In W. Somerset Maugham's The Razor's Edge, published in 1944, the author mentions Parnell and O'Shea: "Passion is destructive. It destroyed Antony and Cleopatra, Tristan and Isolde, Parnell and Kitty O'Shea."

Parnell is a major background character in Thomas Flanagan's 1988 historical novel, The Tenants of Time.

In 1991, Trevor Eve played Parnell in the television mini-series "Parnell and the Englishwoman."

The 1992 novel Death and Nightingales by Eugene McCabe mentions him numerous times.

Lyons points up the dark side as well. The decade-long liaison with Mrs. O'Shea was a disaster waiting to happen, and Parnell had made no preparations for it. He waited so long because of money – there was an expectation that Mrs. O'Shea would receive a large inheritance from her elderly aunt who might have changed her will if she had known about the affair. In the aftermath of the divorce he fought violently to retain control in a hopeless cause. Thereby he ruined his health and wrecked his movement; it never fully recovered. The bottom line for Lyons, however, is positive:

Historian R. F. Foster argues that in the countryside the Land League "reinforced the politicization of rural Catholic nationalist Ireland, partly by defining that identity against urbanization, landlordism, Englishness and—implicitly—Protestantism."

Gladstone described him: "Parnell was the most remarkable man I ever met. I do not say the ablest man; I say the most remarkable and the most interesting. He was an intellectual phenomenon." Liberal leader H. H. Asquith called him one of the three or four greatest men of the 19th century, while Lord Haldane described him as the strongest man the House of Commons had seen in 150 years. Historian A. J. P. Taylor says, "More than any other man he gave Ireland the sense of being an independent nation."