The chairman of the Commons Standards Committee breached the MPs' code of conduct by accepting payment for hosting events for a drug company in Parliament.
But the committee recommended that no further action was required against Sir Kevin Barron following the "minor" and "inadvertent" breach.
The fees received by Sir Kevin Barron after sponsoring three events in Parliament were donated to charity, and Parliamentary Standards Commissioner Kathryn Hudson concluded the breach of the rules was "at the least serious end of the spectrum" because the MP did not personally benefit.
The report recommended that no further action was required against the Labour MP, who stood aside while the committee examined his case, and the inquiry had raised "no doubts over Kevin Barron's integrity and honesty".
Sir Kevin referred himself to the independent commissioner after a Daily Telegraph report on his links to the Japanese Pharmaceutical Group (JPG).
The Rother Valley MP entered into an agreement with JPG in 2011 and subsequently sponsored three events in Parliament.
Money from the JPG was donated to the Bluebell Wood Children's Hospice in his constituency, and the committee's report found that three cheques to the charity, each for £3,000, were registered in Sir Kevin's entry in the Commons register of Members' interests as remuneration for his work for JPG.
In her inquiry, the commissioner found that by hosting the events in Parliament, Sir Kevin breached the Commons "banqueting rules" that state that private dining rooms "are not to be used for the direct or indirect financial or material gain by a sponsor", even though the money went to charity.
That error put Sir Kevin in breach of the MPs' code of conduct, which states that parliamentarians using Westminster's facilities must follow the rules.
Ms Hudson said: "I consider this breach of the rules and the code to be at the least serious end of the spectrum. There was nothing untoward in Sir Kevin booking the dining room for the use of a third party.
"Indeed, at the relevant time the banqueting regulations allowed third parties to book the dining facilities, only through the sponsorship of a named Member.
"The breach of the rules arose because, in his agreement for the provision of services, Sir Kevin said that he might sponsor the occasional event in Parliament. This then became part of the remunerated agreement and thus breached the regulations."
Sir Kevin told the commissioner he was "surprised" at the breach of banqueting rules because he had declared his interests when booking the rooms.
"If I had breached any of these rules I would have expected to be contacted by the registrar," he said.
In its conclusions, the committee agreed with the commissioner that Sir Kevin had "adhered fully to the rules on the disclosure of his relationship" with JPG.
But "we also agree with the commissioner's finding that Kevin Barron was in breach of the code in accepting payment of any kind linked to the use of House facilities".
"Although he did not receive payment himself, he was able to direct that it be given to a particular charity as a result of the contractual relationship.
"This means that the payment was a 'direct or indirect financial or material gain' to Kevin Barron as a sponsor of the events organised in the House on behalf of JPG."
The committee added: "Kevin Barron has cooperated fully with the Commissioner's investigation and we agree with her conclusion that the inquiry has raised no doubts over Kevin Barron's integrity and honesty. We consider that no further action is required."
But the panel, made up of MPs and lay members, raised concerns about the "multiplicity of rules" set by different bodies within the Commons and the "vagueness" of the wording.