In November 2015, Roberts became the longest-serving female parliamentarian in Western Australia's history, breaking the record set by Liz Constable.
She then spent periods as a policy officer for the Departments of Local Government (1989 to 1991) and Occupational Health, Safety and Welfare (1993 to 1994), as well as serving as a board member of the East Perth Redevelopment Authority from 1991 to 1993.
Roberts first ran for parliament at the 1993 state election, standing unsuccessfully for the Legislative Council in fourth place on Labor's ticket in the East Metropolitan Region.
[1] She entered the Legislative Assembly the following year, winning the 1994 Glendalough by-election (caused by the resignation of former premier Carmen Lawrence).
[3] When Geoff Gallop resigned as premier and leader of the Labor Party in January 2006, Roberts was one of three candidates to replace him, along with Alan Carpenter and Jim McGinty.
She was initially given the education portfolio, but in February 2011 was promoted to shadow treasurer, replacing Ben Wyatt (who had unsuccessfully challenged for the leadership).
Roberts herself saw off her 2013 opponent, Daniel Parasiliti, with somewhat less difficulty, picking up a swing of over 12 percent to turn Midland into a safe Labor seat at one stroke.
With former Premier Colin Barnett's retirement from politics in 2018, Roberts became the Mother of the Western Australian Legislative Assembly as its longest-serving member.