The 28-year-old midfielder had also been a target for Glasgow Rangers, managed by former Bees boss Mark Warburton but it came to no fruition.
Leeds’ offer was accepted and Diagouraga has agreed personal terms and signed a two-and-a-half year deal at Elland Road.
He could make his debut at Griffin Park when Leeds visit Brentford tomorrow.
Paris-born Diagouraga was one of Brentford’s longest-serving players, having first joined the club in January 2010 on loan from Peterborough.
He made 226 appearances for the Bees and was voted the supporters’ player of the year last season for his key role in helping the team reach the Championship play-offs.
Diagouraga was under contract at Griffin Park until June 2017, having signed his last deal in December 2014.
Once on the books of Paris St-Germain as a teenager, Diagouraga moved to Watford aged 17 and at one stage in 2005 was reportedly a target for Chelsea.
He made a handful of appearances for the Hornets’ first team, while spending time on loan at Swindon, Rotherham and Hereford.
He later made the Hereford move permanent before joining Peterborough, and later Brentford.
Diagouraga will wear the No.16 shirt and he travelled with the rest of the squad today for the trip to Brentford for the fixture on Tuesday evening.