A native of Hope River, Sullivan had a career as an assistant editor at the Charlottetown Herald as well as a lawyer before being elected to the provincial legislature in 1872 as a Liberal MLA.

Sullivan reorganised the Conservative Party and was asked by the lieutenant governor to become premier once Davies' coalition broke up and became unable to command a majority in the assembly.

He protested the federal government's failure to fulfill the terms of confederation on which the island had joined the dominion in 1873.

In 1886, he petitioned the Imperial government in London protesting Canada's delinquency in respect to promises to ensure communication lines between the island and the rest of the country but the problem remained unresolved until the 1900s.

In 1914 he was made a Knight Bachelor by King George V. Note: Interim leaders are shown in italics