Haggerty, 28, re-joins the club having originally signed as a 16 year old following spells in Super League with Salford and Harlequins and joins on a 12 month deal.
The Irish international said: “I’m really excited about coming back to Widnes and meeting up with some familiar faces, I didn’t really want to leave in the first place! I can’t wait to work with Paul Cullen and Terry O’Connor and am already looking forward to the 2010 season.
Young forward Gerrard, 19, who joins from Wigan, has represented England at Academy level and has signed a two year contract with the Vikings.
Vikings’ Head Coach Paul Cullen added, “I’m delighted to welcome an experienced forward like Gareth and an exciting youngster like Chris to the Club.
“Both will add a great deal to our 2010 squad and with the recruitment process continuing we will certainly be in the mix next season. Let’s not forget it’s the best team on the pitch, not on paper, that will be picking up the trophies!”