He said he was paid "a generous amount" at Greensill, "far more than I was as prime minister".
Greensill, 44, appeared before the Treasury Committee on Tuesday (11) and insisted he took "full responsibility" for the company's collapse.
Ms Eagle also confronted the former Prime Minister on how many times he used one of Greensill's private jets to fly to or from Newquay, close to his third home, or any other non-business declarations.
"The fact that I have this serious economic interest, that's important, but I don't think the amount is particularly germane to answering those questions, and as far as I'm concerned it's a private matter", he told MPs.
Since then it has emerged that Cameron repeatedly lobbied senior government and Bank of England officials previous year to try and help Greensill gain access to COVID support schemes.
"I have spent most of my adult life in public service, I believe in it deeply", he told MPs.
He added: "I think I met him twice while I was in Downing Street and I can absolutely confirm at no stage did he ever suggest that I would go and work with him or for him afterwards".
"I did not believe in March or April, when I was doing this contact, that there was a risk of Greensill falling over", he said.
Tory MP Mel Stride, chairman of the Treasury Committee, questioned whether Mr Cameron's "opportunity to make a large amount of money was under threat" as he sent a "barrage" of messages to government figures last spring when the pandemic broke.
Mr Cameron says Greensill was a "UK fintech potential success story" and that was what he thought was "interesting" about the firm.
The ex-prime minister said it was a "great regret" that Greensill - who he joined as an adviser in August 2018 - collapsed into insolvency earlier this year and that he was "desperately sorry" over the firm's demise.
"I had a big economic investment in the future of Greensill, so I wanted the business to succeed, I wanted it to grow", Cameron said.
The former Conservative leader, who was an adviser to the company and reportedly held lucrative stock options that are now worthless, appeared before a parliamentary committee probing his lobbying ahead of the loan company's collapse in March.
But Mr Cameron insisted that the NHS pay scheme was meant to "stamp out payday lending" by allowing staff to access money they had learnt.
However there has been criticism of how a former prime minister was able to exploit his personal contacts with former colleagues and officials in the pursuit of commercial gain.
In an exchange with Mr Gove, the former prime minister messaged: "Am now speaking to Rishi first thing tomorrow".
He insisted there was "absolutely no wrongdoing" in his lobbying attempts, but accepted that former prime ministers must "act differently".
Asked about one of his messages about Greensill - to Treasury permanent secretary Sir Tom Scholar which ended "love DC" - Mr Cameron said he often used the sign-off.
In documents published Tuesday by the committee, the ex-prime minister and his office staff sent ministers and officials dozens of emails, texts and WhatsApp messages a year ago relating to Greensill, bypassing official channels.
"My children tell me that you don't need to sign off text messages at all and it's very old fashioned and odd to do so".