Johnny Mercer has quit as veterans minister, a Downing Street spokeswoman confirmed.
The former British Army officer was reported to be unhappy about a lack of progress in dealing with former personnel being investigated for killings during the Troubles in Northern Ireland.
He has been heavily involved in the Overseas Operations (Service Personnel and Veterans) Bill, which is going through its final stages in Parliament.
The legislation was developed in response to legal claims made after operations in Iraq and Afghanistan, but does not cover incidents in Northern Ireland.
Prime Minister Boris Johnson thanked the MP for Plymouth Moor View for his service as a minister following his resignation on Tuesday, according to a No 10 spokeswoman.
The statement released shortly after 7pm said: "This evening the Prime Minister has accepted the resignation of Johnny Mercer as minister for defence people and veterans.
"He thanks Johnny Mercer for his service as a Government minister since 2019."