Despite an early lesbian affair, she married the author Peter Forster in 1958, but later accepted her lesbian identity and was divorced.
She came out publicly in 1969 when she joined the Campaign for Homosexual Equality (CHE) and went to serve on its Executive Committee.
She was on the first gay march in the UK in August 1971.
In 1972 she was one of the founders of the Sappho social group and its associated magazine. Sappho (magazine) was published from 1972 to 1981, although the group continued to meet regularly for many more years. Sappho group members used to meet in The Chepstow pub in Notting Hill and had public speakers such as Maureen Duffy and Anna Raeburn.
After Sappho, Jackie became a member of the Greater London Council's Women's Committee.
From 1992 till her death she was an active member of the Lesbian Archive and Information Centre management Committee. In 1997 a BBC film crew came to the archive to film Jackie for a programme about her life which was to be part of the Day That Changed My Life series.
On 6 November 2017, which would have been her 91st birthday, she was the subject of a Google Doodle.
- "Jackie Forster: a legend among lesbians", Brighton Ourstory.
- "Jacqueline Mackenzie", Internet Movie Database.
- "Who was Jackie Forster and how did she pioneer gay rights as a reporter?", Metro, 6 November 2017.