Peter Cruddas donated £500,000 on February 5, just three days after being admitted to the House of Lords.
Lord Cruddas had previously failed the Appointments Commission vetting process, only for the Prime Minister to overrule its advice and make him a Lord.
Now the SNP’s Westminster deputy leader Kirsten Oswald has accused the Prime Minister of setting up donors with “jobs for life”.
She said: “It’s business as usual for Boris Johnson’s sleaze-ridden Tory government as it continues to line its pockets with dodgy donations.
“The half-a-million-pound donation from a Tory peer straight after his appointment to the Lords, despite concerns from the watchdog, is clear for all to see – a corrupt Tory government handing out jobs for the boys.
“Boris Johnson has been more willing to set up his friends and Tory party donors with jobs for life, while thousands of businesses and families across the UK are struggling to make ends meet as a result of the pandemic.
“These latest revelations of cronyism will certainly not be the last, but they make clear that this Tory government is driven by its own interests.”
Mr Johnson was criticised for approving Lord Cruddas's appointment in December after the commission raised "historic concerns” over allegations made during the peer’s time as Conservative Party treasurer.
This related to allegations published in The Sunday Times in 2013 that he offered access to former prime minister David Cameron in exchange for donations.
Mr Cruddas denied the claim, but it was found to be true by the Court of Appeal following a libel case.
The court found the allegation against Mr Cruddas made by The Sunday Times to be untrue.
Labour chairwoman Anneliese Dodds has also now accused Mr Johnson of "incredible sleaze".
She said: “Peter Cruddas resigned as Tory Treasurer amidst allegations of cash for access.
"He failed the Lords vetting process, but Boris Johnson made him a peer anyway.
"He made a £500,000 donation to the Tories a few days later. Incredible sleaze from the PM."
Shadow chancellor of the Duchy of Lancaster Angela Rayner claimed the appointment "stinks".
She said: "What do the Tories do for a man forced to resign in disgrace amidst allegations of cash for access to government ministers?
"They put him in the House of Lords with a life peerage and he coincidentally gives the Tories half a million quid."
Defending the appointment, Mr Johnson said: "The most serious accusations levelled at the time were found to be untrue and libellous."
A Conservative Party spokesperson said: "Donations to the Conservative Party are properly and transparently declared to the Electoral Commission and are published by them.
"Fundraising is a legitimate part of the democratic process. The alternative is more taxpayer-funding of political campaigning, which would mean less money for frontline services like schools, police and hospitals – or else, being in the pocket of union barons, like the Labour Party."