O’Carroll, 25, who only moved to Hull from Wigan in the close season, joins the Vikings on a two-and-a-half-year deal.
The Ireland international made 10 appearances at Hull, and trained with his new team mates for the first time today, Friday, and could go straight in to Denis Betts’ squad for Monday’s Super League clash with Castleford.
He said: “I had a few offers from elsewhere and normally I wouldn’t have entertained the opportunity of joining a club part-way through the season but as soon as Widnes came in for me, I jumped at the chance and I was keen to put pen to paper as quickly as possible.
“Before signing the contract, I spoke at length with Paul Cullen and he brought me right up to speed with the clubs plans. What he had to say excited me and I definitely want to be a part of the future here at Widnes.”
The Oldham-born forward made 61 appearances for Wigan, where he worked under current Widnes coach Denis Betts, and assistant Dave Banks.
Betts said: “We’re really fortunate to have secured Eamon, not only for the rest of this season but the following two as well. This affords him ample opportunity to get used to our systems and the way we go about our business here at Widnes, which will hopefully bring out the best in him.
“He is a fantastic player who never gives less that 100% on the pitch. We actually tried hard to bring him to the Stobart Stadium before his move to Hull FC, but unfortunately we entered the party a little too late and the deal was already in the bag.”