Tocqueville, who despised the July Monarchy (1830–1848), began his political career in 1839. From 1839 to 1851, he served as deputy of the Manche department (Valognes). In parliament, he defended abolitionist views and upheld free trade, while supporting the colonisation of Algeria carried on by Louis-Philippe's regime. Tocqueville was also elected general counsellor of the Manche in 1842, and became the President of the department's conseil général between 1849 and 1851. According to one account, Tocqueville's political position became untenable during this time in the sense that he was mistrusted by both the left and right, and was looking for an excuse to leave France.

In 1831, he obtained from the July Monarchy a mission to examine prisons and penitentiaries in America, and proceeded there with his lifelong friend Gustave de Beaumont. While Tocqueville did visit some prisons, he traveled widely in America and took extensive notes about his observations and reflections. He returned within nine months, and published a report, but the real result of his tour was De la démocratie en Amerique, which appeared in 1835. Beaumont also wrote an account of their travels in Jacksonian America: Marie or Slavery in the United States (1835). During this trip he made a side trip to Lower Canada to Montreal and Quebec City from mid August to early September 1831.

De Tocqueville believed that the American jury system was particularly important in educating citizens in self-government and rule of law. He often expressed how the civil jury system was one of the most effective showcases of democracy because it connected citizens with the true spirit of the justice system. In his 1835 treatise, Democracy in America, he explained:

Although Tocqueville had favoured retention of distinct traditional law, administrators, schools, etc., for Arabs who had come under French control, he judged the Berber tribes of Kabylie (in his second of Two Letters on Algeria, 1837) as "savages" not suited for this arrangement; they would best be managed, he argued, not by force of arms, but by the pacifying influences of commerce and cultural interaction.

Tocqueville's views on the matter were complex. Even though in his 1841 report on Algeria he applauded Bugeaud for making war in a way that defeated Abd-el-Kader's resistance, he had advocated in the Two Letters that the French military advance leave Kabylie undisturbed, and in subsequent speeches and writings he continued to oppose intrusion into Kabylie.

In the debate about the 1846 extraordinary funds, Tocqueville denounced Bugeaud's conduct of military operations, and succeeded in convincing the Assembly not to vote funds in support of Bugeaud's military columns. Tocqueville considered Bugeaud's plan to invade Kabylie, despite the opposition of the Assembly, as a seditious act in the face of which the government was opting for cowardice.

In his 1847 Report on Algeria, Tocqueville declared that Europe should avoid making the same mistake they made with the European colonization of the Americas in order to avoid the bloody consequences. More particularly he reminds his countrymen of a solemn caution whereby he warns them that if the methods used towards the Algerian people remain unchanged, colonization will end in a blood bath.

During the Second Republic, Tocqueville sided with the parti de l'Ordre against the socialists. A few days after the February insurrection, he believed that a violent clash between the Parisian workers' population led by socialists agitating in favor of a "Democratic and Social Republic" and the conservatives, which included the aristocracy and the rural population, was inescapable. As Tocqueville had foreseen, these social tensions eventually exploded during the June Days Uprising of 1848.

A supporter of Cavaignac and of the parti de l'Ordre, Tocqueville, however, accepted an invitation to enter Odilon Barrot's government as Minister of Foreign Affairs from 3 June to 31 October 1849. There, during the troubled days of June 1849, he pleaded with Jules Dufaure, Interior Minister, for the reestablishment of the state of siege in the capital and approved the arrest of demonstrators. Tocqueville, who since February 1848 had supported laws restricting political freedoms, approved the two laws voted immediately after the June 1849 days, which restricted the liberty of clubs and freedom of the press.

Tocqueville had supported Cavaignac against Louis Napoléon Bonaparte for the presidential election of 1848. Opposed to Louis Napoléon's 2 December 1851 coup which followed his election, Tocqueville was among the deputies who gathered at the 10th arrondissement of Paris in an attempt to resist the coup and have Napoleon III judged for "high treason", as he had violated the constitutional limit on terms of office. Detained at Vincennes and then released, Tocqueville, who supported the Restoration of the Bourbons against Napoleon III's Second Empire (1851–71), quit political life and retreated to his castle (Château de Tocqueville).

Assimilation, however, was the best solution for Native Americans and since they were too proud to assimilate, they would inevitably become extinct. Displacement was another part of America's Indian policy. Both populations were "undemocratic", or without the qualities, intellectual and otherwise, needed to live in a democracy. Tocqueville shared many views on assimilation and segregation of his and the coming epochs, but he opposed Arthur de Gobineau's theories as found in The Inequality of Human Races (1853–55).

In 1855, he wrote the following text published by Maria Weston Chapman in the Liberty Bell: Testimony against Slavery

In 1856, Tocqueville published The Old Regime and the Revolution. The book analyzes French society before the French Revolution—the so-called "Ancien Régime"—and investigates the forces that caused the Revolution.

A longtime sufferer from bouts of tuberculosis, Tocqueville would eventually succumb to the disease on 16 April 1859. He was buried in the Tocqueville cemetery in Normandy.

Tocqueville advocated racial segregation in Algeria with two distinct legislations, one for European colonists and one for the Arab population. Such a two-tier arrangement would be fully realised with the 1870 Crémieux decree and the Indigenousness Code, which extended French citizenship to European settlers and Algerian Jews, whereas Muslim Algerians would be governed by Muslim law and restricted to a second-class citizenship.

The above is often misquoted as a slavery quote because of previous translations of the French text. The most recent translation from Arthur Goldhammer in 2004 translates the meaning to be as stated above. Examples of misquoted sources are numerous on the internet; the text does not contain the words "Americans were so enamored by equality" anywhere.

Tocqueville was quoted in several chapters of Toby Young's memoirs, How to Lose Friends and Alienate People, to explain his observation of widespread homogeneity of thought even amongst intellectual elites at Harvard University, during his time spent there. He is frequently quoted and studied in American history classes. Tocqueville is the inspiration for Australian Novelist Peter Carey in his 2009 novel, Parrot and Olivier in America.

According to Tocqueville, assimilation of Black people would be almost impossible and this was already being demonstrated in the Northern states. As Tocqueville predicted, formal freedom and equality and segregation would become this population's reality after the Civil War and during Reconstruction – as would the bumpy road to true integration of Black people.

Tocqueville believed that jury Service not only benefited the society as a whole, but enhanced jurors’ qualities as citizens. Because of the jury system "they were better informed about the rule of law, and they were more closely connected to the state. Thus, quite independently of what the jury contributed to dispute resolution, participation on the jury had salutary effects on the jurors themselves."