Roland van Hauwermeiren, 68, resigned as the charity’s director in Haiti amid accusations he used sex workers while delivering humanitarian aid to the region.
Speaking for the first time since he fled his home in Poperinge, on the Belgian-French border, he said: “I’m a man of flesh and blood and I have made mistakes.
“I am deeply ashamed.”
Mr van Hauwermeiren said he quit because he did not exercise enough control over staff accused of sexual misconduct.
Describing his sexual encounters in Haiti, the Belgian said: “I have indeed admitted to an inquiry group that I had intimate contact up to three times.
“I thought it was with a mature, honourable lady – she was not an earthquake victim and not a prostitute.
“I never gave her money.”
It is claimed Oxfam covered up findings into the behaviour of its staff and Archbishop Desmond Tutu is the latest high-profile ambassador to leave the charity in the wake of the scandal.
His office said he was “deeply disappointed” and “saddened by the impact of the allegations on the many thousands of good people who have supported Oxfam’s righteous work”.
Mr van Hauwermeiren said: “There are things that are described correctly.
“But there are many lies and exaggerations.
“Parties every week? Fancy villas? Women paid with money from the organisation?”
“I never visited a brothel, nightclub or bar in the city or this country.
“There were also frequent attempts by ladies and gentlemen to enter my house with all sorts of excuses for asking money, demanding a job or offering sexual services.
“I never accepted those advances.”
Meanwhile, International Development Secretary Penny Mordaunt held talks yesterday with National Crime Agency chief Lynne Owens on stamping out sexual exploitation overseas.
The scandal has seen support grow for a petition to end a commitment requiring Britain to spend at least 0.7 per cent of national income overseas each year.
It has almost 50,000 signatures and needs a similar number to force a parliamentary debate.
To sign the petition visit https://petition.parliament.uk/petitions/200292