The feisty 46-year-old player, who was as famous for winning matches as he was for losing his temper during them, will star in a series of print ads created by M&C Saatchi.
The ads, to run in the US, Canada and Latin America, liken the star to the Travelex brand and will be used to promote the firm's corporate service targeting senior finance executives.
In a broader marketing effort, McEnroe will also attend events for Travelex clients as well as featuring in online, outdoor and direct mail advertising.
He joins British & Irish Lions rugby star and World Cup winner Jonny Wilkinson who was signed for a two-year deal in June with ads using the strapline "Travelex hate to be beaten too".
Australian cricket team captain Adam Gilchrist still represents the brand after being signed in 2003.
On signing Wilkinson in June, Travelex hinted that a third ambassador to promote its American businesses would be added later this year.
McEnroe continues to play in seniors' tennis tournaments but has developed a media career, with mixed success. He fronted the short-lived gameshow 'The Chair' and a failed talk show on CNBC in the US last year, but continues to be a favourite at Wimbledon for his commentary on the BBC.
His last sponsorship deal was for Bic razors in his early tennis career.
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