From 1986, he was a director of Richmond Savings Credit Union, and from 1995 to 1998, he served as board chair. He is a past director of Coast Capital Savings. Before becoming a Member of the Legislative Assembly (MLA), Ken was serving the City of Richmond in his third term as a City councillor.
As an MLA, Johnston served as a member of the Government Caucus Committee on Government Operations. He also served on Legislative Standing Committees: Parliamentary Reform, Ethical Conduct, Standing Orders and Private Bills, Legislative Initiatives, and he was a member of the Special Committee to Review the Freedom of Information & Protection of Privacy Act. He previously served on the Health and Crown Corporations committees.
Ken and Diane Johnston married in 1972 in Fraserview and have two grown children, Scott and Jennifer.