Gageby grew up in the Shankill area of Belfast, and worked in a mill from the age of eleven.
[2] In 1898, he was one of six trade unionists elected to the Belfast Corporation, with the backing of the Independent Labour Party.
[1] On the council, he represented the Shankill ward, and chaired the Baths and Lodging House Committee.
Soon after the election, Gageby was invited to London, where he discussed with Winston Churchill the possibility of opening a Labour Exchange in Belfast.
He remained in this department until the Government of Northern Ireland was established, after which time he worked for its Ministry of Labour.