Lib Dem MP David Laws should be suspended from the Commons for seven days over his expenses claims, the Commons standards watchdog has said.
A report ruled the former Chief Secretary to the Treasury was "guilty of a series of serious breaches of the rules, over a considerable time".
He wrongly claimed expenses to pay rent to his partner and for building work and telephone bills, the report said.
Mr Laws apologised and said his motivation was to protect his privacy.
The commissioner recommended that Mr Laws' suspension should begin on 7 June, but MPs will be asked to vote on whether to approve the sanction on 16 May.
Mr Laws won praise from his Conservative colleagues for his role in coalition negotiations and his work on tackling the budget deficit in the short time he worked alongside Chancellor George Osborne.
But he resigned after just 17 days as a cabinet minister, following reports he had claimed about £40,000 to pay rent to his partner, the lobbyist James Lundie.
Payments to relations and partners have been against parliamentary rules since 2006.
Mr Laws paid back £56,592 - more than was eventually required of him by the Parliamentary Standards Commissioner - and referred himself for investigation.
In a 280-page report, the commissioner concluded that the Yeovil MP had committed "a series of serious breaches" of the rules, including the rule on paying partners.
The report also said Mr Laws had been wrong to designate his constituency home as his "main home" because he was spending more time living in London at Mr Lundie's property.
This arrangement allowed him to claim thousands of pounds in allowances against Mr Lundie's property.
He was also found to have wrongly claimed some £2,000 for building work and £2,248 for telephone bills. The rent claimed on Mr Lundie's property was also found to be £200 to £300 higher a month than the market rate.
The standards commissioner accepted Mr Laws' motivation was to keep his homosexuality secret, but said that nonetheless, his conduct "was not above reproach" and he had given "a false impression" of his relationship with his landlord.
"I have no evidence that Mr Laws made his claims with the intention of benefiting himself or his partner in conscious breach of the rules. But the sums of money involved were substantial... Some of them continued over a number of years."
He said Mr Laws clearly recognised there was "potential conflict between the public interest and his private interest" and "his desire for secrecy led him to act in a way which was not compatible with the standards expected of an MP".
"It was inappropriate for him to be judge and jury in his own cause," he added.
The commissioner accepted that Mr Laws' claims would have been "considerably more" if he had stuck to the rules, and he agreed that there was no loss to the taxpayer from the breaches.
He added that Mr Laws' behaviour since May 2010 had been "exemplary" and it was "to his credit" that he had repaid the money.
Following the publication of the report, Mr Laws said in a statement to the Commons: "I take complete and personal responsibility for the mistakes I made and apologise without reservation to the House and my constituents.
"This last year has been a difficult one for me and I am grateful for all the support I've received.
"Each of us should be our own sternest critic, and all of us in this place want to see the reputation of this House restored after the last few disastrous years.
"If by my actions I've contributed in any way to further undermining the reputation of this House I can only apologise without reservation."
David Cameron said he believed Mr Laws was "a very talented individual" and added: "I think he has a lot to offer public life and I hope he stays in public life."
Asked about Mr Laws' possible return to front-line politics, the prime minister said he wanted to study the commissioner's report and "take it from there".
Deputy Prime Minister Nick Clegg said Mr Laws was "a good friend" and "a close colleague" who had "always been upfront about the fact that he made mistakes".
"Motives are important," he said. "The expenses scandals in the past were about some individuals who were fleecing the system for financial benefit and I don't believe that was ever, ever David's motive."
Senior Labour backbencher Frank Field criticised the decision by the standards and privileges committee to suspend Mr Laws.
"Today's report vividly highlights how arbitrary these judgements are," he said. "MPs guilty of milking the system get a ticking off. David Laws, whom the report accepts was not guilty of this, and who has already lost office for a year, is further punished with a suspension."