Chapman was born in Surrey but moved to Darlington at a young age where she attended Hummersknott School and Queen Elizabeth Sixth Form College,before studying psychology at Brunel University, and later took an MA in archaeology at Durham University. She has worked as a prison psychologist..
Chapman worked as senior parliamentary researcher for Darlington Labour MP Alan Milburn. After a career break, she returned to politics at Darlington Borough Council when she was elected as borough councillor for the Cockerton West ward in 2007.
In November 2009, Chapman was selected as one of four candidates to succeed Milburn as Labour's parliamentary candidate for Darlington on an open shortlist. She was selected to stand for parliament by the local constituency party the following month. Chapman said: "This shows that the people of Darlington want to choose a Darlington person who will put the town first." She was elected Darlington MP in the 2010 general election with a majority of 3,388. As a result of her election victory, she decided to stand down as a councillor.
Chapman made her maiden speech in Parliament on 7 June 2010, during which she asked for social network services to be regulated to stop pedophiles. She also backed the Building Schools for the Futureprogramme. Chapman is also a Vice Chair of the Blairite organisation Progress