He was later promoted to become the Head of the Policy Unit from 2001 until being created a life peer in 2005, when he was appointed Minister of State for Education in HM Government.

[8] Adonis has worked for a number of think tanks, is a board member of Policy Network and is the author or co-author of several books, including several studies of the British class system, the rise and fall of the Community Charge, and the Victorian House of Lords.

[9] Shortly thereafter Adonis and his sister were placed in care, because their father was working long hours and was not able to cope with sole parental responsibilities.

[10] Adonis studied at Keble College, Oxford, where he graduated with a first-class Bachelor of Arts degree in Modern History in 1984.

[11] He pursued further studies at Oxford and undertook a Doctor of Philosophy (DPhil) degree at Christ Church, which he completed in 1988 with a thesis entitled The political role of the British peerage in the Third Reform Act system, c.

In May 2009, while reviewing potential cycle "super highways" with Kulveer Ranger and then-London Mayor Boris Johnson, the group had a narrow escape when a passing lorry's back door "suddenly flew open, dragged a parked car into the street and smashed into another – just feet from the group".

In this role, he pioneered the plan for High Speed 2, the proposed high-speed railway line from London to Birmingham and the north of England.

In July 2015, Adonis was appointed a non-executive director to HS2 Board Ltd.[22] Adonis planned and announced the electrification of the Great Western Main Line from London Paddington to Bristol, Cardiff and Swansea, and the electrification of lines in North West England from Manchester to Liverpool and Manchester to Preston.

He was reputed to favour a Lib–Lab deal and, given his SDP background, was a member of Labour's negotiating team that attempted to form an administration with the Liberal Democrats.

After the Liberal Democrats formed a coalition government with the Conservative Party, Adonis stepped down from frontline politics.

[24] Adonis left the Institute for Government in January 2012, to become Chair of Progress, an internal Labour Party organisation.

[32] Adonis considered standing[33] to be Labour's candidate for Mayor of London in 2016, but ended his putative campaign in February 2015, endorsing Tessa Jowell.

[34] In October 2015, he resigned the Labour Party whip in the House of Lords to sit as a non-affiliated Peer and lead a newly created National Infrastructure Commission (NIC).

However, he resigned from the NIC in December 2017 because of HM Government's approach to Brexit, saying the UK was "hurtling towards the EU's emergency exit with no credible plan for the future of British trade and European co-operation".

In his resignation letter, he wrote that, as well as Brexit, the recent decision to end the InterCity East Coast rail franchise three years early, at a cost of hundreds of millions of pounds, would also have forced him to quit.

[40] In May 2021, Adonis called for Tony Blair to return to frontline politics in the wake of a poll being released showing Labour 15% behind the Conservatives.