Labour's Lord Clarke of Hampstead has been told to apologise to the House of Lords after being found to have claimed money to which he was not entitled.
An inquiry by a Lords committee found the peer had claimed expenses for overnight stays in London when he was not in the capital.
Lord Clarke was investigated by police as part of their inquiry into alleged misuse of expenses by parliamentarians.
Prosecutors chose not to bring charges against him due to lack of evidence.
Lord Clarke has already repaid £9,190 for claims judged to be inappropriate.
But the Lords Privileges Committee has urged him to "apologise without reservation for his misuse of the [reimbursement] scheme" after he was found to be "at fault" over his claims.
Following an inquiry, the Lords authorities found he had breached rules entitling him only to claim for expenses incurred in staying overnight in London when away from his main home on parliamentary business.
It said Lord Clarke - who, like all peers, is not paid a salary - had acknowledged that he had claimed expenses on occasions when he had returned to his main home between sittings.
It also noted that, in a letter to the authorities in February, Lord Clarke said he believed he was "entitled" to claim subsistence for overnight stays after conversations with Labour's Chief Whip in the Lords and other peers.
Lord Clarke, who became a life peer in 1998, has decided not to appeal against the committee's ruling.
To date, three MPs and one peer have been charged with expenses abuses, although all four deny any wrongdoing.
Prosecutors are currently considering a further two cases involving unnamed politicians after receiving files from the police on them.
In addition to Lord Clarke, the Crown Prosecution Service decided not to bring charges against fellow Labour peer Baroness Uddin following a police investigation.