 After graduating, she worked as a political staffer, prior to working as an articled clerk at Slater & Gordon in 2001; she then worked as a campaign organiser for the Australian Labor Party (2001–2004).Between 2004 and 2007, she practised as a solicitor with Slater & Gordon, specialising in asbestos litigation and industrial law.Firth was elected as a councillor of the City of Sydney in 2004.