Cardiff chairman Mehmet Dalman tonight confirmed a deal had been struck for Adeyemi to join Leeds.
The midfielder, 23, joined the Bluebirds for a fee in excess of £1m region from Birmingham City in 2014, but he struggled to make an impact in South Wales, with his last appearance for the club coming last March.
The box-to-box midfielder started his career at Norwich City and he played under new Leeds head coach Uwe Rosler at Brentford as the club suffered play-off final heartbreak against Yeovil in 2013.
Adeyemi travelled to Leeds on Monday for talks and a medical and it is thought a move to the Whites, initially on a season-long loan, will be confirmed on Tuesday.
Rosler has been in the market for a new central midfielder after the club lost Luke Murphy for the opening month of the season to a knee injury.
Jamaican midfielder Rudy Austin was released on a free at the end of last season.