Following his demotion in 2013, Byrne continued to serve in junior Shadow Ministerial roles under Miliband and later Jeremy Corbyn.

Byrne was the Labour candidate for Mayor of the West Midlands in 2021, losing to the Conservative incumbent Andy Street.

[5] Prior to his election to Parliament, he worked for Accenture and Rothschild & Co, before co-founding a venture-backed technology company, e-Government Solutions Group, in 2000.

Byrne was selected to contest the Birmingham Hodge Hill by-election following the resignation of the veteran Labour MP Terry Davis to become the Secretary-General of the Council of Europe.

[11][12] A vocal campaigner for Road Safety, Byrne handed a petition in to Parliament in 2005 demanding tougher punishments for dangerous drivers.

He sat on the parliamentary committee that shaped the Road Safety Act 2006, which increased fixed penalty fines for driving while using a mobile.

[13] Following the 2006 local elections, he was promoted in place of Hazel Blears as Minister of State for Policing and Counter-terrorism at the Home Office.

[14][12] However, just a fortnight later Home Secretary John Reid transferred him to the Immigration role, switching portfolios with Tony McNulty.

This change was controversial because it applied retrospectively to immigrants who had entered Britain under the old rules, meaning the British Government had "moved the goalposts"–a degree became effectively an essential requirement, regardless of the skills or economic contribution that an individual could demonstrate.

[23] In June 2008, Byrne suggested the "August bank holiday" be made a weekend of national celebration in a speech to a New Labour think tank.

Scotland's August bank holiday being held on a different date from that in Wales and England, he later retracted his suggestion – after pressure from the Scottish National Party – saying he was merely trying to "get the debate started".

[26] Byrne later claimed that it was just typical humour between politicians but regretted it since the new government used it to justify the wave of cuts that were introduced.

Byrne was sacked after increasing criticism from Labour members and having "badly lost the confidence of the PLP", particularly after allegedly describing the Conservative-led coalition's benefits cap as "too soft",[37] saying that "Ministers have bodged the rules so the cap won't affect Britain's 4,000 largest families and it does nothing to stop people living a life on welfare".

[48] In April 2022, Byrne was found to have bullied a staff member; he was suspended from the House of Commons for two days after a 22-month investigation.

Byrne denied wrongdoing, but the Independent Parliamentary Standards Authority (IPSA) found there was "overwhelming evidence" that a member of Byrne's staff had worked on his failed mayoral election campaign during office hours, conservatively estimating that at least around 1,000 hours of public-funded time had been spent on the campaign.

[54] On the Chancellor Address to the Kings Speech Byrne called on the Reeves to encourage further measures including promotion of business the help civic society, review of all investments and shares held by the government[55] In February 2020, Byrne was selected as the Labour candidate for the 2021 West Midlands mayoral election.

[57] In his campaign he called for the Birmingham 2022 Commonwealth Games to be the "greenest games ever",[58] and pledged to be the first West Midlands Mayor to fill the role of Deputy Mayor with a woman[59] and to revitalise the West Midlands' ailing car industry by positioning it at the heart of British electric vehicle manufacturing.