Peel saw part-time military Service as a captain in the Manchester Regiment of Militia in 1808, and later as lieutenant in the Staffordshire Yeomanry Cavalry in 1820.

Peel entered politics in 1809 at the age of 21, as MP for the Irish rotten borough of Cashel, Tipperary. With a scant 24 electors on the rolls, he was elected unopposed. His sponsor for the election (besides his father) was the Chief Secretary for Ireland, Sir Arthur Wellesley, the Future Duke of Wellington, with whom Peel's political career would be entwined for the next 25 years. Peel made his maiden speech at the start of the 1810 session, when he was chosen by Prime Minister Spencer Perceval to second the reply to the king's speech. His speech was a sensation, famously described by the Speaker, Charles Abbot, as "the best first speech since that of william Pitt."

As chief secretary in Dublin in 1813, he proposed the setting up of a specialist police force, later called "peelers". In 1814 the Royal Irish Constabulary was founded under Peel.

For the next decade he occupied a series of relatively minor positions in the Tory governments: Undersecretary for War, Chief Secretary for Ireland, and chairman of the Bullion Committee (charged with stabilising British finances after the end of the Napoleonic Wars). He also changed constituency twice: first picking up another constituency, Chippenham, then becoming MP for Oxford University in 1817.

Peel married Julia Floyd (daughter of General Sir John Floyd, 1st Baronet) on 8 June 1820. They had seven children:

Peel was considered one of the rising stars of the Tory party, first entering the cabinet in 1822 as Home Secretary. As Home Secretary, he introduced a number of important reforms of British Criminal law: most memorably establishing the Metropolitan Police Force (Metropolitan Police Act 1829) for London. It was the enabling legislation for the first English police force, the "bobbies" (in England) or "peelers" (in Ireland), which served as the model for modern urban police departments throughout England. He also reformed the Criminal law, reducing the number of crimes punishable by death, and simplified it by repealing a large number of Criminal statutes and consolidating their provisions into what are known as Peel's Acts. He reformed the gaol system, introducing payment for gaolers and education for the inmates.

He helped in the repeal of the Test and Corporation Acts in May 1828. They required many officials to be communicants in the Anglican Church and penalised both nonconformists and Catholics. They were no longer enforced but were a matter of humiliation. Peel at first opposed the repeal but reversed himself and led the repeal, after consultation with Anglican Church Leaders. In Future religious issues he made it a point to consult with church Leaders from the major denominations.

It was in 1829 that Peel established the Metropolitan Police Force for London based at Scotland Yard. The 1,000 constables employed were affectionately nicknamed 'bobbies' or, somewhat less affectionately, 'peelers'. Although unpopular at first, they proved very successful in cutting crime in London, and by 1857 all cities in the UK were obliged to form their own police forces. Known as the father of modern policing, Peel developed the Peelian Principles which defined the ethical requirements police officers must follow to be effective. In 1829, when setting forth the principles of policing a democracy, Sir Robert Peel declared: "The police are the public and the public are the police."

The middle and working classes in England at that time, however, were clamouring for reform, and Catholic Emancipation was only one of the ideas in the air. The Tory ministry refused to bend on other issues and were swept out of office in 1830 in favour of the Whigs. The following few years were extremely turbulent, but eventually enough reforms were passed that King william IV felt confident enough to invite the Tories to form a ministry again in succession to those of Lord Grey and Lord Melbourne in 1834. Peel was selected as prime minister but was in Italy at the time, so Wellington acted as a caretaker for three weeks until Peel's return.

The Tory Ministry was a minority government and depended on Whig goodwill for its continued existence. Parliament was dissolved in December 1834 and a general election called. Voting took place in January and February 1835 and Peel's supporters gained around 100 seats, but this was not enough to give them a majority.

As his statement of policy at the general election of January 1835, Peel issued the Tamworth Manifesto. This document was the basis on which the modern Conservative Party was founded. In it Peel pledged that the Conservatives would endorse modest reform.

In May 1839 he was offered another chance to form a government, this time by the new monarch, Queen Victoria. However, this too would have been a minority government, and Peel felt he needed a further sign of confidence from his Queen. Lord Melbourne had been Victoria's confidant since her accession in 1837, and many of the higher posts in Victoria's household were held by the wives and female relatives of Whigs; there was some feeling that Victoria had allowed herself to be too closely associated with the Whig party. Peel therefore asked that some of this entourage be dismissed and replaced with their Conservative counterparts, provoking the so-called Bedchamber Crisis. Victoria refused to change her household, and despite pleadings from the Duke of Wellington, relied on assurances of support from Whig Leaders. Peel refused to form a government, and the Whigs returned to power.

Peel finally had a chance to head a majority government following the election of July 1841. His promise of modest reform was held to, and the second most famous bill of this ministry, while "reforming" in 21st-century eyes, was in fact aimed at the reformers themselves, with their constituency among the new industrial rich. The Factory Act 1844 acted more against these industrialists than it did against the traditional stronghold of the Conservatives, the landed gentry, by restricting the number of hours that children and women could work in a factory and setting rudimentary safety standards for machinery. Interestingly, this was a continuation of his own father's work as an MP, as the elder Robert Peel was most noted for reform of working conditions during the first part of the 19th century. Helping him was Lord Shaftesbury, a British MP who also established the coal mines act.

As an aside in reference to the repeal of the Corn Laws, Peel did make some moves to subsidise the purchase of food for the Irish, but this attempt was small and had little tangible effect. In the age of laissez-faire, government taxes were small, and subsidies or direct economic interference were almost nonexistent. That subsidies were actually given was very much out of character for the political times; Peel's successor, Lord John Russell, received more criticism than Peel on Irish policy. The repeal of the Corn Laws was more political than humanitarian. Peel's support for free trade could already be seen in his 1842 and 1845 budgets; in late 1842 Graham wrote to Peel that "the next change in the Corn Laws must be to an open trade" while arguing that the government should not tackle the issue. Speaking to the cabinet in 1844, Peel argued that the choice was maintenance of the 1842 Corn Law or total repeal. Despite all of Peel's efforts, his reform programs had little effect on the situation in Ireland.

In 1843 Peel was the target of a failed assassination attempt; a criminally-insane Scottish wood turner named Daniel M'Naghten stalked him for several days before killing Peel's personal secretary Edward Drummond thinking he was Peel which led to the formation of the Criminal defense of insanity.

The Historian Boyd Hilton argues Peel knew from 1844 he was going to be deposed as the Conservative leader. Many of his MPs had taken to voting against him, and the rupture within the party between liberals and paternalists which had been so damaging in the 1820s, but masked by the issue of parliamentary reform in the 1830s, was brought to the surface over the Corn Laws. Hilton's hypothesis is that Peel wished to actually be deposed on a liberal issue so that he might later lead a Peelite/Whig/Liberal alliance.

The most notable act of Peel's second ministry, however, was the one that would bring it down. Peel moved against the landholders by repealing the Corn Laws, which supported agricultural revenues by restricting grain imports. This radical break with Conservative protectionism was triggered by the Great Irish Famine (1845–1849). Tory agriculturalists were sceptical of the extent of the Problem, and Peel reacted slowly to the famine, famously stating in October 1846 (already in opposition): "There is such a tendency to exaggeration and inaccuracy in Irish reports that delay in acting on them is always desirable".

His own party failed to support the bill, but it passed with Whig and Radical support. On the third reading of Peel's Bill of Repeal (Importation Act 1846) on 15 May, MPs voted 327 votes to 229 (a majority of 98) to repeal the Corn Laws. On 25 June the Duke of Wellington persuaded the House of Lords to pass it. On that same night Peel's Irish Coercion Bill was defeated in the Commons by 292 to 219 by "a combination of Whigs, Radicals, and Tory protectionists". Following this, on 29 June 1846, Peel resigned as prime minister.

Peel was thrown from his horse while riding on Constitution Hill in London on 29 June 1850. The horse stumbled on top of him, and he died three days later on 2 July at the age of 62 due to a clavicular fracture rupturing his subclavian vessels.

Julia, Lady Peel, died in 1859. Some of her direct descendants now reside in South Africa, the Australian states of New South Wales, Queensland, Victoria and Tasmania, and in various parts of the United States and Canada.

Peel often started from a traditional Tory position in opposition to a measure, then reversed his stance and became the leader in supporting liberal legislation. This happened with the Test Act, Catholic Emancipation, the Reform Act, income tax and, most notably, the repeal of the Corn Laws as the first two years of the Irish famine forced this resolution because of the urgent need for new food supplies. Peel, a Conservative, achieved repeal with the support of the Whigs in Parliament, overcoming the opposition of most of his own party. Many critics accordingly saw him as a traitor to the Tory cause, or as "a Liberal wolf in sheep's clothing", because his final position reflected liberal ideas. Historian A.J.P. Taylor says: "Peel was in the first rank of 19th century statesmen. He carried Catholic Emancipation; he repealed the Corn Laws; he created the modern Conservative Party on the ruins of the old Toryism."