Midfielder Grant became Boro's first summer signing in May 2012 when he put pen to paper on a three-year contract, which began in July that year.
Born in Chester-le-Street, Leadbitter joined hometown club Sunderland as a 16-year-old and progressed through the ranks to spend four seasons in the side as an attacking midfielder.
He played 111 league games for the Black Cats, scoring 11 goals.
Former Ipswich manager Roy Keane paid £2.6m to bring Leadbitter from his old club Sunderland to Portman Road in summer 2009 and the player spent three seasons in East Anglia, making 116 league appearances and scoring 13 goals.
Grant turned down a number of alternative offers to join Boro after his Ipswich contract ended.
An experienced junior international, he made three appearances for England U-21s.
After winning the Middlesbrough Official Supporters Club Player of the Year award for 2012/13, he added the Middlesbrough Disabled Supporters Association's Player of the Year award for 2013 at a ceremony in January 2014.
Boro's current captain, Leadbitter formed an uncompromising midfield partnership with Adam Clayton as the club earned promotion to from the Championship in the 2015-16 season.