Hillier was a junior government minister from 2007 until 2010 and was succeeded by Caroline Flint as Shadow Secretary of State for Energy and Climate Change in the Labour Party October 2011 reshuffle.

[6] In 2004, Hillier was selected as the Labour prospective parliamentary candidate to contest Hackney South and Shoreditch through an all-women shortlist.

In March 2008, Hillier voted with the Government in favour of nationwide Post Office closures, including seven in Hackney, of which her constituency forms a part.

[21] An ardent supporter of the Remain campaign during the 2016 EU referendum, Hillier announced that she was "devastated" that the United Kingdom voted to leave the European Union and that the decision was fuelled by "xenophobic undertones".

[22] She supported Owen Smith in the failed attempt to replace Jeremy Corbyn in the 2016 Labour Party leadership election.

[26] Hillier was appointed Dame Commander of the Order of the British Empire (DBE) in the 2021 Birthday Honours for political and parliamentary service.

[30] Hillier has written about her opposition to assisted dying and the Terminally Ill Adults (End of Life) Bill, raising concerns about how it would be policed.