Mr O'Donnell, 37, a former American footballer, has signed up as managing director and deputy head of equities in Europe for Salomon Smith Barney in London. He will start his new job on 1 July.
Mr O'Donnell was not available to explain his change of heart. But given that it takes six years to train for the Catholic priesthood, he had clearly not got very far towards that goal.
Robert DiFazio, the head of European equities at Salomon Smith Barney to whom Mr O'Donnell will report, said yesterday: "We are delighted that Jim has opted to return to the securities business and even more so that he has chosen SSB as the firm to provide him with this opportunity.
"He is an extraordinary talent who will bring leadership and an extensive knowledge of industry to the firm."
His original decision to turn his back on a lucrative career to pursue a higher calling hit the headlines last year.
As a priest in New York, he could have expected to take home a salary of less than pounds 6,000 a year, less than 1 per cent of what he was earning on Wall Street.
Mr O'Donnell, an American citizen who holds a Bachelor Degree in Comparative Religion from Princeton, spent 11 years in the City before returning to New York in 1993 to head up HSBC Securities.
A spokesman for the Catholic Media Office reacted stoically to the news: "It is important for Christians to be in the workplace, in some cases more important.
"Christianity is not something that should just be practiced behind seminary walls."