Lord Levy, Tony Blair's envoy to the Middle East, has said he will step down when the PM leaves office in June.
Lord Levy was appointed Mid East envoy by Mr Blair
He said his departure "has always been anticipated and is not different to many other similar positions."
Lord Levy was arrested in recent months by police investigating cash for honours, but denies any wrongdoing.
Downing St thanked him for his role, saying the PM "believes, and has always said, that Lord levy has done an excellent job as his personal envoy."
Lord Levy's spokesman said: "He is deeply honoured and privileged to have served his country in the international arena in the past nine years and is grateful to the PM for this opportunity.
"He also pays tribute to the three foreign secretaries he has worked with - the late Robin Cook, Jack Straw and Margaret Beckett and all the ambassadors and staff at the Foreign Office past and present for their tireless energy, hard work and support."
Lord Levy also congratulated Gordon Brown on becoming the next prime minister, a job he will take over on 27 June, "and wishes him well in all his future endeavours as PM".
Lord Levy was arrested on suspicion of possible infringements of honours and election laws in July 2006, and, six months later, arrested again on suspicion of conspiracy to pervert the course of justice.
His arrests came during a year-long inquiry into allegations that honours had been sold.
Police handed their 216-page report to the Crown Prosecution Service in April. Mr Blair was among 136 people interviewed by Scotland Yard. They all deny any wrongdoing.
BBC political correspondent Jo Coburn said it was assumed that Lord Levy would give up his fundraising role as well.