He made his first team debut on 25 February 2006 in a 1–0 home win over Plymouth Argyle, coming on as a late substitute for Kevin Lisbie.
In January 2007, he joined Conference side Halifax Town for a month,[6] scoring his first senior goal on his debut against York City.
[7] Soon after his return to Derby, he joined League Two side Wycombe Wanderers on loan until the end of the season,[8] where he made seven appearances before being recalled in April.
[16] On 16 November 2008, Watford caretaker manager Malky Mackay named Ainsworth as one of three players that were to be loaned to other clubs to gain match fitness.
After making his first start for the Bees, against Yeovil in April 2010, he got in trouble with the club's manager Andy Scott, having gone straight down the tunnel after being substituted.
[26] He made his league debut for Shrewsbury Town on 7 August 2010, with a man of the match performance in a 3–1 victory against Bradford City on the opening day of the 2010–11 season.
[33] He scored his first goal for the club on his debut on 11 August 2012, in a League Cup game against Hull City, in which Rotherham lost 7–6 on penalties after drawing 1–1 against the Championship side.
[40] In the UEFA Europa League second qualifying round second leg match away against Stjarnan, Ainsworth scored his first European goal, but Motherwell lost 3–2, being eliminated 5–4 on aggregate.
[41] In May 2015, Ainsworth scored in both legs as Motherwell defeated Rangers 6–1 on aggregate in the Scottish Premiership Play-off Final to retain their place in the top flight.
[47][48][49] In August 2019, Ainsworth dropped down two divisions to join National League South side Weymouth,[citation needed] which had been newly promoted.
[51] Following a brief spell with Weymouth, Ainsworth went onto feature for the likes of Dulwich Hamlet, Welling United, Braintree Town and Heybridge Swifts before ultimately joining AFC Sudbury in July 2022.