Haddington trained at the Bristol Old Vic Theatre School from 1975–77.
She appeared as Professor Docherty in the third-season finale of Doctor Who entitled "Last of the Time Lords". Haddington's other TV credits include Life Begins, Foyle's War as Hilda Pierce, A&E, Cracker, Holby City, Wire in the Blood, Coronation Street, Midsomer Murders, The Musketeers, Taggart, Scott & Bailey and The Bill in which she played two different roles, the first in 1997 and the second in 2007.
In 2011 and 2013 she appeared as Carol Porter in the Sky1 comedy series The Café.
In 2013, she appeared as Madame Dupin in the BBC TV miniseries Spies of Warsaw.
In 2015, she played Gina Corbin in Ordinary Lies and Fanny Biggetywitch in Dickensian.
In 2017 Haddington played Julia's mother Marion in Graham Linehan's Motherland.
