Louise Haigh has resigned as transport secretary after pleading guilty for wrongly reporting her work mobile phone was stolen in 2013.
In a letter to Sir Keir Starmer, Haigh said she was “totally committed to our political project” but that it would be "best served by my supporting you from outside government”.
Her resignation comes a day after admitting she had told police her phone was lost in a mugging but later found it had not been taken.
Ms Haigh said the incident was a "genuine mistake" and was advised by a lawyer "not to comment" during a police interview. Her case was referred to the Crown Prosecution Services.
The transport secretary pleaded guilty to a false report to police at a magistrates' court six months before becoming an MP in the 2015 election, and received a discharge - the "lowest possible outcome".
According to Whitehall sources, Ms Haigh declared her discharge on appointment to the shadow cabinet when Labour was in opposition.
The prime minister has since thanked her for her work to deliver the government's transport agenda.