Paynter, 28, was placed on the transfer list by Neil Warnock at the end of last season after a frustrating two years at Elland Road.
Paynter was signed by former Leeds boss Simon Grayson in the summer of 2010, but had been restricted to 28 appearances, scoring three goals.
The former Swindon forward, who began his career at Port Vale and also had spells at Hull, Southend, Bradford and Brighton - the latter two on loan - struggled with injury when he first arrived at Elland Road and made only four appearances last season, scoring twice in the 4-1 win over Peterborough in April.