He became leader of the Alberta New Democratic Party in 1984, succeeding Grant Notley who had died in a plane crash. Martin led the party to a highwater mark winning 16 seats in the 1986 provincial election, making him leader of the opposition in the legislature. The NDP matched this performance in the 1989 election. In 1993, the party was wiped out, and Martin was defeated in his riding, Edmonton Norwood, by Liberal Andrew Beniuk. He quit the party's leadership in 1994.
Martin returned to the Legislative Assembly of Alberta as the NDP Member of the Legislative Assembly (MLA) for Edmonton Beverly Clareview after an absence of eleven years by winning a seat in the 2004 general election. However, he was defeated in his 2008 campaign for re-election by Progressive Conservative Tony Vandermeer.
Martin was defeated when he later ran as an NDP candidate in the 1997 and 2000 federal elections in the Edmonton North and Edmonton Centre-East ridings. He is currently the NDP candidate in the riding of Edmonton East for the next Federal Election.