John Pinkerton was born in Seacon More, County Antrim. He rose to prominence as a member of Ballymoney Debating and Agricultural Societies, and as a radical member of Coleraine Board of Guardians. In 1885 he contested the election for North Antrim as an Independent candidate. Though defeated, he impressed the Parnellites and was adopted as party candidate for Galway in 1886. He won the election, and held the seat until 1900.