The Liberal Democrat MP faces a seven-day suspension from the Commons after the Standards and Privileges Committee found he committed "a series of serious breaches of rules".
In a personal statement to the House of Commons, Mr Laws apologised for deliberately concealing the fact that he was using allowances to pay his partner James Lundie rent. But he insisted his only motive had been to avoid being outed as gay, rather than financial profit.
The watchdog's report was published nearly a year after the arrangement emerged publicly and Mr Laws was forced to quit as Chief Secretary to the Treasury.
It is the toughest punishment handed to an MP since Tory Derek Conway was suspended for 10 days in 2008 after paying his sons for work they had not done.
However, despite the strong criticism of Mr Laws' actions, ministers and senior politicians expressed sympathy and suggested he could still make a comeback.
At a joint event in east London, David Cameron and his Lib Dem deputy, Nick Clegg, praised the former banker as a "very talented individual" and a "good friend".
The Prime Minister said: "I have made clear just from knowing him as I do and dealing with him, I do think he has a lot to offer public life. I hope he stays in public life."
Mr Clegg added: "David Laws is a good friend and a close colleague. We do need to look at the report but his motives, he has always been very open about his motives.
"They were about protecting his own privacy, not financial gain. I think that is very important when we pass judgment on people, is to look at the 'why' - not just the 'what', but also the 'why'."
Lib Dem Business Secretary Vince Cable said he wanted to see Mr Laws "back in action" as soon as possible.
"I've worked with him over many years and he's a very able, talented person," he told Sky News. "I'm sure we will see him back."
Tory Education Secretary Michael Gove said: "It is my personal hope that we will all be able once more to make use of his (Mr Laws') talents in the country's service before too long."
Meanwhile, ex-Lib Dem leader Lord Ashdown questioned whether the suspension was in line with punishments meted out to other politicians over expenses abuses.
"Is it right for somebody like (Labour former home secretary) Jacqui Smith, who broke the rules and financially gained, to be treated with an oral apology, and someone like him - who broke the rules and saved the public (£30,000) - to be given a sanction like this?" the peer said on ITV News.
Labour backbencher Frank Field also waded in to criticise the "arbitrary nature" of expenses judgments. Some MPs who "milked the system" got a "ticking off", while Mr Laws had not benefited financially and was suspended.
But Labour frontbencher Chris Bryant branded the response to Mr Laws' punishment "sanctimonious".
Posting on social networking site Twitter, Mr Bryant said: "There seems to be one Laws for a Lib Dem and another for the rest. I really don't buy this argument, but it's the sanctimony that I can't stand."
Mr Bryant also questioned whether there had ever been an MP who was allowed to serve in government again after being suspended from the Commons.
After being elected to Parliament in 2001, Mr Laws designated his Somerset house as his main home.
That meant he could claim thousands of pounds in rent and other costs for Mr Lundie's London flat, where they both lived.
In July 2007, the lobbyist sold the flat and bought another property in the capital - financing the purchase partly with a £99,000 gift from Mr Laws.
Standards Commissioner John Lyon found that "any reasonable person properly seized of the facts" would agree Mr Laws had been in breach of rules against using expenses to rent from a partner, which were introduced in July 2006.
However, he went further and concluded that from April 2005 the MP was wrong to designate his Somerset home as his main home, because he was spending more time with Mr Lundie in London.
Mr Lyon also said the MP had misled the Commons authorities since 2001 by filing documents which gave a "false impression" of his relationship with Mr Lundie.
"Mr Laws' wish to maintain his personal privacy cannot, in my view, justify - although it may explain - such conduct," the commissioner added.
The MPs accepted that Mr Laws could have made higher claims had he been open about his living arrangements, and used expenses to run his substantial Somerset home.
But they added: "While it is clear that Mr Laws could have arranged his affairs in a way which was less good value for money, we do not agree that the criterion of value for money should be established by comparing his potential claims with his actual claims."
Mr Laws was found to have paid his partner up to £370 per month above the market rent, and used expenses to contribute £2,000 to building works at the second London property they shared.
The report also revealed that Mr Laws admitted regularly putting in expenses claims just below the £250 threshold which would have meant receipts were required.
The MP told the commissioner: "I didn't want to send in bills with his name on. It was an aspect of my secrecy."
Despite the evidence of excessive claims, the committee did not order Mr Laws to hand back any money because he has already repaid £56,592 - the full amount of his second home allowance claims between July 2006 and July 2009.
The Commons will debate the report on Monday, with Mr Laws' suspension expected to begin on June 7.
Flanked by Lib Dem MPs, the ex-minister told a hushed chamber that he took "complete and personal responsibility" for his mistakes.
"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 then I can only apologise without reservation."
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