The 38-year-old midfielder had trained with the U’s during the summer of 2019 but ended up signing for A-League side Newcastle Jets in Australia last term.
“Hunger is there to get it right,” Hoolahan BBC Radio Cambridgeshire said.
“I take care of myself, do the right things and hope to feel good. I wake up, I’m hungry and I’m relatively fit, I’ll stay active as long as I can, I love playing football and it’s been a part of me since I was a kid.”
Born in Dublin, Hoolahan played 112 Premier League games for Norwich City, in which he made 352 appearances, and represented Blackpool and West Brom among his senior clubs.
A member of Martin O’Neill’s Irish side that has reached the last 16 Euro 2016 games, scoring in a 1–1 draw with Sweden and finishing centre-out Robbie Brady headed to seal a 1-0 win over Italy.
U-coach Mark Bonner said on the club’s website: “We’re very pleased that Wes has joined us and the quality and delight it will bring us into a strong addition to the team.”