Ernest Murray says Marois, who was elected premier in 2012, didn't know he approached someone at the Roche firm until after the fact.
Marois, whose minority government was defeated in this year's provincial election, was Opposition leader at the time.
Murray told the inquiry headed by Justice France Charbonneau he approached the firm just before the 2008 provincial election when he found he was having difficulty hitting his fundraising target in Marois's Charlevoix riding.
He knew an engineer at Roche and asked for $10,000.
After a while, the engineer indicated he was ready to donate the money but wanted names to put on the cheques.
Murray suggested the names of three people he trusted. In the end they weren't contacted by Roche.
Instead, the firm supplied most of the $10,000 in cheques signed by other people.
Murray says he later told Marois about his effort.
"Financing was my responsibility," he told the commission. "I was responsible. I put her in a bit of trouble for doing this. I can't say it was my finest hour but there it is."
Murray said he told her how he solicited the Roche engineer for $10,000 but he couldn't remember if he mentioned the three names he had provided to the firm.
"We're proud, we want to reach (the financing targets) and we do things," he said. "Madame Marois woke up with this in her hands. The deed was already done."
In a series of emails dated March 2009 that were produced at the commission, the Roche engineer made a link between the political contributions and two contracts the firm was seeking to obtain in the region northeast of Quebec City.
One concerned a museum and the other a junior college. The engineer wrote that Roche would like "at least one of the two."
The PQ was not in power at that time and had no control over the awarding of contracts.
Murray referred the engineer to the local people responsible for the contracts.
He also stressed that firms were always treated equally, with little regard to political contributions.
Murray said the information he gave Roche had already been made public by the government.
He also pointed out that even when in power, the PQ received less money than the Liberals from engineering firms.
Under cross-examination by PQ lawyer Estelle Tremblay, Murray said the party did not know what he was doing and would not have approved had it been aware.
"I was not authorized to do this," by either Marois or the party, he said.
In Quebec City, interim PQ leader Stephane Bedard expressed disappointment at the allegations and said he has asked the party to do whatever to find out the names of the donors in question.
"If there is money that needs to be reimbursed, we will do so."