Her grandfather, Frederick Mallalieu, had been Liberal Member of Parliament for Colne Valley.

He was succeeded in that seat by her uncle, Lance Mallalieu, later Labour MP for Brigg.

Mallalieu fought Hitchin for Labour at both the February and October 1974 elections, but was defeated by the Conservative Ian Stewart on both occasions.

In a House of Lords debate on the European Union (Withdrawal) Bill on 31 January 2018 Baroness Mallalieu revealed she had voted for Britain to leave the European Union in the 2016 referendum.

Lady Mallalieu is a member of the Exmoor Hunt and the Devon and Somerset Staghounds.