Peel entered politics at the young age of 21 as MP for the Irish rotten borough of Cashel, Tipperary. With a scant 24 voters 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 the 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."

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 stabilizing 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. He later served as MP for Tamworth from 1830 until his death. His home of Drayton Manor has since been demolished.

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). 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 resigned as Home Secretary after the Prime Minister, Lord Liverpool, became incapacitated and was replaced by George Canning. Canning favoured Catholic Emancipation, while Peel had been one of its most outspoken opponents (earning the nickname "Orange Peel"). Canning himself died less than four months later and, after the brief premiership of Lord Goderich, Peel returned to the post of Home Secretary under the premiership of his long-time ally the Duke of Wellington. During this time he was widely perceived as the number-two in the Tory Party, after Wellington himself.

However, the pressure on the new ministry from advocates of Catholic Emancipation was too great and an Emancipation Bill was passed the next year. Peel felt compelled to resign his seat as MP representing the graduates of Oxford University (many of whom were Anglican clergymen), as he had stood on a platform of opposition to Catholic Emancipation (in 1815 he had, in fact, challenged to a duel the man most associated with emancipation, Daniel O'Connell). Peel instead moved to a rotten borough, Westbury, retaining his Cabinet position. Peel's protégé Gladstone later emulated Peel by serving as MP for Oxford University from 1847 to 1865, before himself being defeated for his willingness to disestablish the Irish Church.

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' (both terms are still used today). 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 in order to be effective. His most memorable principle was, "the police are the public, and the public are the police."

The Middle and Working Classes in England at that time, however, were clamoring 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 the three weeks until Peel's return.

This new Tory Ministry was a minority government, however, and depended on Whig goodwill for its continued existence. As his statement of policy at the general election of January 1835, Peel issued the Tamworth Manifesto. The issuing of this document is often seen as one of the most crucial points at which the Tories became the Conservative Party. In it he pledged that the Conservatives would endorse modest reform, but the Whigs instead formed a compact with Daniel O'Connell's Irish Radical members to repeatedly defeat the government on various bills. Eventually Peel's ministry resigned out of frustration and the Whigs under Lord Melbourne returned to power. The only real achievements of Peel's first administration was a commission to review the governance of the Church of England. This ecclesiastical commission being the forerunner of the Church Commissioners. A further achievement was a rapid gain in seats in the House of Commons which was around 100 seats in the 100 days Peel's Ministry lasted.

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 for several years, 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 coterie 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 came to office during an economic recession which had seen a slump in world trade and a budget deficit of £2.5 million run up by the whigs. Confidence in Banks and Businesses was low and a trade deficit existed. To raise revenue Peel's 1842 budget saw the re-introduction of Income Tax, removed previously at the end of the Napoleonic War. The money raised was more than expected and allowed for the removal and reduction of over 1,200 tariffs including the controversial sugar duties. It was also in the 1842 budget that the repeal of the corn laws was first proposed. It was defeated 4:1.

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. In 1843 Peel was the target of a failed assassination attempt; a criminally insane Scottish woodsman named Daniel M'Naghten stalked him for several days before accidentally killing Peel's personal secretary Edward Drummond instead.

The most notable act of Peel's second ministry, however, was the one that would bring it down. This time 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. As realisation dawned, however, he hoped that ending the Corn Laws would free up more food for the Irish. 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.

Though he knew repealing the laws would mean the end of his ministry, Peel decided to do so. It is possible that Peel merely used the Irish Famine as an excuse to repeal the Corn Laws as he had been an intellectual convert to free trade since the 1820s. Blake points out that if Peel were convinced that total repeal was necessary to stave off the famine, he would have enacted a bill that brought about immediate temporary repeal, not permanent repeal over a three-year period of gradual tapering-off of duties. The historian Boyd Hilton argues Peel knew from 1844 he was going to be deposed as Conservative leader — many of his MPs had taken to voting against him and the rupture within the party between liberals and paternalist which had been so damaging in the 1820s, but masked by the issue of 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.

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 non-existent. 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.

He did retain a hard core of supporters however, known as Peelites, and at one point in 1849 was actively courted by the Whig/Radical coalition. He continued to stand on his conservative principles, however, and refused. Nevertheless, he was influential on several important issues, including the furtherance of British free trade with the repeal of the Navigation Acts. Peel was a member of the committee which controlled the House of Commons Library, and on 16 April 1850 was responsible for passing the motion that controlled its scope and collection policy for the rest of the century.

Peel was thrown from his horse while riding up 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. His Peelite followers, led by Lord Aberdeen and William Gladstone, went on to fuse with the Whigs as the Liberal Party.

Peel married Julia, youngest daughter of General Sir John Floyd, 1st Baronet, in 1820. They had five sons and two daughters. Four of his sons gained distinction in their own right. His eldest son Sir Robert Peel, 3rd Baronet, served as Chief Secretary for Ireland from 1861 to 1865. His second son Sir Frederick Peel was a politician and railway commissioner. His third son Sir William Peel was a naval commander and recipient of the Victoria Cross. His fifth son Arthur Wellesley Peel was Speaker of the House of Commons and created Viscount Peel in 1895. His daughter Julia married the 6th Earl of Jersey. Julia, Lady Peel, died in 1859.