Before joining the ACTU, McManus was the Branch Secretary and an organiser with the Australian Services Union (ASU) in NSW and the ACT.

[citation needed] McManus went to Carlingford High School and studied for a Bachelor of Arts in philosophy at Macquarie University.

[6] In 2012, McManus founded the Destroy The Joint campaign formed in response to radio broadcaster Alan Jones' criticism of then Prime Minister Julia Gillard and other prominent women.

Her first television interview as Secretary sparked controversy, when McManus refused to back down from the use of illegal industrial action as a method of union campaigning.

[14] Prior to the 2019 federal election, McManus led the union movement's "Change the Rules" campaign, which pushed for workplace rights.

[19] McManus is an enthusiastic player of computer games, and describes herself as "the definition of a total gamer", who has been playing since the DOS era.