[2] Garrett was born and raised in northern Melbourne and was educated at Radford College[3] followed by the Australian National University, where she studied law.

Jane became an Associate to Justice Alan Boultan of the Australian Industrial Relations Commission in 1997, was an articled clerk with Holding Redlich in 1998, a union officer with the Transport Workers' Union in 1999, a senior adviser to Steve Bracks from 2000 to 2004 and a lawyer at Slater and Gordon from 2004 to 2010.

[11] In November 2016, Garrett announced on a Facebook post that she had recently undergone a successful operation for breast cancer, and would be taking four months' leave from parliament for treatment and recovery.

[13][14] On 27 September 2017, Garrett announced she would not contest Brunswick at the next state election, and would seek preselection for the Victorian Legislative Council seat of Western Metropolitan Region.

[15] Her preselection bid was unsuccessful, with Labor's left faction backing Ingrid Stitt, branch secretary of the Australian Services Union.