Mr Cruddas was dismissed from the role after the Sunday Times reported that he was charging £250,000 to meet Mr Cameron but has since won a libel action against the newspaper.
High Court judge Mr Justice Tugendhat criticised the Prime Minister’s response, saying he had subjected his former Conservative colleague to a “public humiliation”.
Mr Cameron said he was “very sorry” about the treatment of Mr Cruddas, who claimed he was “cut off” by the party.
He also said he had been “made to feel like an outcast” by the Prime Minister.
Mr Cameron added that he was looking forward to meeting his former colleague later in the year.
He said: “I rather think I do owe him an apology”, adding: “Had I known at the time how badly the journalists had behaved, I might have been in the position to take a different approach. I am very sorry about that.
“I congratulate Peter Cruddas on his victory and on the verdict he has won. I think it is very deserved.
“He has done a huge amount for this country. I look forward to meeting him after the summer.”
Six weeks ago, the High Court also awarded Mr Cruddas £180,000 in damages and ordered the newspaper to pay £500,000 in costs.