The 26-year-old winger Ainsworth was on loan from Rotherham last season and scored 11 goals - with 12 assists - to help them finish runners-up to Celtic in the SPFL Premiership for the second consecutive season.
The Fir Park club claimed to have seen off competition for Ainsworth's signature from north and south of the border, as well as overseas. After signing his new deal with the Lanarkshire side, Ainsworth said: "I'm very happy. I've had a summer thinking about what's going to happen and to be honest I never wanted to leave.
"I'm happy to have it sorted and I love the club. In the short space of time I've been here, everyone in and around the club have been brilliant and I feel at home here.
"I managed to hit the ground running last year and hopefully I can carry that on to next season.
"It would be amazing if I could score more goals next season and get more assists but I know I have to go out there and give my all to keep my spot in the team. We achieved great things last year and I'm sure we can go out and do it again."
Stuart McCall, the Motherwell manager, was delighted to secure the services of Ainsworth. "He made such a massive contribution last season, particularly around Christmas and New Year when he was flying high and practically unplayable in certain games," McCall said.
"To have such a scoring threat from midfield is vital for any side, but he also contributes by creating goals for our strikers. With a strong pre-season behind him and the platform of playing in the Europa League to look forward to, it should be a big season for him."
Meanwhile, Hutchinson ended his association with Motherwell by joining Sky Bet Championship side Fulham on a two-year deal.