[3] He served under the Earl of Liverpool, George Canning and Lord Goderich as Under-Secretary of State for War and the Colonies from 1821 to 1827 and was sworn of the Privy Council in 1827.

Wilmot-Horton's aide-de-camp at the Colonial Office was his friend Thomas Moody, Kt., with whom he maintained an extensive correspondence throughout his life.

In this position he pushed for a plan where so called paupers gave up their rights to parish maintenance in return for grants of land in the colonies.

[1] In 1831 Wilmot-Horton was made a Knight Grand Cross of the Royal Hanoverian Order by William IV and appointed Governor of Ceylon.

In Ceylon he implemented the recommendations of the Colebrooke–Cameron Commission forming Ceylon's First Legislative Council and Executive Committee; abolished the feudal practice of compulsory labour; abandoned government's claims to free service (Rajakariya); recognised the right to private property; abolished government's monopoly of the Cinnamon trade, dating to the Dutch period; started the first newspaper of Ceylon, the Colombo Journal, and the first mail coach in Asia ; reformed the education system, established Ceylon's first public school, the Colombo Academy, which was renamed in 1881 as the Royal College, the only school in the world outside England, to be granted approval by Queen Victoria to use the word Royal in a college name.

[citation needed] In his absence his plans on assisted emigration were ridiculed as those of an impractical dreamer by a succession of writers on colonial affairs, but Wilmot-Horton continued to write pamphlets advocating and defending his ideas.

[1] Wilmot-Horton died at Sudbrook Park, Petersham, in May 1841, aged 56, and was succeeded in the baronetcy by his eldest son, Robert.