The young lawyer moved his growing family to Annapolis Royal, where he set up a successful law practice and proceeded to build the local support needed to launch a political career. In 1826, he ran for and was elected to a seat in the House of Assembly. When his father died in 1829, Haliburton was appointed to his father's seat on the bench as a judge in the Inferior Court of Common Pleas. In 1841, Haliburton was elevated to the Supreme Court of Nova Scotia. In addition to his judicial duties, Haliburton also took an active part in the business life of Windsor. He was owner of six stores and wharfage, the investor in a gypsum mine, president of the Windsor Agricultural Society, and president of a company which owned the Avon River Bridge. A wealthy and respected man, Haliburton had a great deal of influence on contemporary social and political issues.

Yet, the liberal Tory in Haliburton was deeply frustrated. The strict code of conduct imposed on him as a member of the conservative ruling elite did not allow him to express his strongly held progressive views. Since he and his family would suffer serious repercussions to their personal welfare if he challenged the established ruling elite directly, Haliburton decided to anonymously create a fictional character to act as his mouthpiece. And so Sam Slick came into being.

Haliburton's slick con man and keen observer of Nova Scotian life was introduced in 1835. The high-spirited and irreverent Sam Slick first charmed readers from the pages of The Nova Scotian, the newspaper published by Haliburton's friend, Joseph Howe. Sam was so popular that Howe issued the twenty-one newspaper instalments in book form the following year. Audiences on both sides of the Atlantic wanted more. Haliburton yielded to public pressure and wrote two more Nova Scotia-based series of adventures for Sam; the second in 1838 and the third in 1840. Sam then left Nova Scotia to be an attache to England in an 1843 collection but he returned to Nova Scotia as a fisheries agent in an 1853 two-volume work. With its sequel in 1855, Haliburton retired his fictional mouthpiece. Sam had served his creator well for twenty years.

Haliburton is best known as the creator of Sam Slick, the most popular comic figure in nineteenth century English literature. His effective use of colourful regional dialect, racy free-flowing dialogue, and conflicting narrative voices to create humorous situations was innovative and influenced the development of a distinctive American humour. His contributions to literature were recognized in 1858 by Oxford University when Haliburton was the first colonial writer to be awarded an honorary degree in literature.

In addition to his Sam Slick series, Haliburton also wrote four histories, the most ambitious being the first full-length history of Nova Scotia, An Historical and Statistical Account of Nova Scotia (1829). Other non-fiction works published by Haliburton included a number of political pamphlets and a full-length work on Canada and colonial policy, The Bubbles of Canada (1839).

Haliburton also wrote several successful fiction titles that did not employ Sam Slick. The Old Judge (1849) centres on the travels of a Windsor judge while The Season-Ticket (1860) is a series of conversations held by a railway season ticket holder in England. In a writing career that spanned thirty-seven years, Haliburton wrote 18 major works and established himself as a major figure in nineteenth-century English literature.