An abrasive openside flanker, Heenan captained the New Zealand Under-20s when they finished runners-up to South Africa in the 2012 IRB Junior World Championship last summer.
The former Whangarei Boys High School First XV captain went on to sign for Auckland and was a member of the Blues development programme.
Incoming Connacht head coach Pat Lam spoke about the young forward he spotted at an early age, saying: "I came across Jake when he was 17-years-old. He played for the Blues Under-18 team when they won the national competition and, even then, I could see what a natural leader and genuine team player he was.
"He brought those leadership skills, as well as his physicality, to the Under-20 World Championship last summer with the Baby Blacks.
"Jake is highly regarded back in New Zealand and it is a real coup for Connacht to catch him. I'm very much looking forward to working with him when he arrives here in early July."