Robinson served in the role of General Secretary of the DUP from 1975, a position which he held until 1979 and which afforded him the opportunity to exert unprecedented influence within the fledgeling party. In 1977, Robinson was elected as a councillor for the Castlereagh Borough Council in Dundonald, and in 1979, he became one of the youngest Members of Parliament (MP) when he was narrowly elected for Belfast East. He held this seat until his defeat by Naomi Long in 2010, making him the longest-serving Belfast MP since the 1800 Act of Union.