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Forbes' annual survey of National Football League teams' valuations put the Cowboys at £2.6bn.
It means the American Football side go above Real Madrid, who had topped the magazine's annual poll of the world's most valuable franchises in July.
The Spanish club now trail the Cowboys by £500m according to the new figures.
Last year the Cowboys' revenue was £402m, a record for a US sports team.
Forbes also puts the Cowboys' rise to the number one spot down to the "shrewd" marketing of owner Jerry Jones and the revenue from their home ground, the AT&T Stadium.
The team have the highest NFL average attendance (90,000) and the stadium brings in £78m in revenue from matchday tickets every season and £19m from other events.
The Cowboys have not reached the Super Bowl for 19 years but this is the ninth consecutive year that the Cowboys have been the most valuable NFL team.
The average NFL team is now worth £1.3bn according to Forbes, a 38% increase on last year.
Forbes say one reason is the revenue from their TV deal which last year saw the 32 teams share £2.9bn in national broadcasting revenue.
Dallas Cowboys have overtaken Real Madrid as the world's most valuable sports team, according to business magazine Forbes.