The duo join previously-announced Jessie J and will.i.am on the show, which is based on hit Dutch format The Voice of Holland.
"I'm excited about The Voice, and thrilled to be participating as a coach," Jones said. "This is a strong show; it's all about talent - but it's also exciting, competitive and compelling television. I've been blessed over the years to share the stage with some of the world's finest artists, and I look forward to being part of the team that discovers a great, new, genuine talent."
O'Donoghue, who has sold over 3.5 million albums worldwide as lead singer of the Irish group, said: "I'm a massive fan of The Voice, so to be involved as a coach is amazing.
"This is a show unlike any other because it puts vocal ability first above all else. I look forward to putting my team together and battling it out with the other coaches to see who wins this unique, credible competition. I'm in it to win it!"
Of the completed lineup, BBC One controller Danny Cohen added: "I'm delighted to be announcing Tom Jones and Danny O'Donoghue as coaches for The Voice. Tom is a music legend and will bring huge experience and creativity to the lineup. Danny is a rising star who will bring freshness and surprise to the team.
"Overall, our lineup of Tom Jones, Jessie J, will.i.am and Danny O'Donoghue gives us mega-star quality, great musical range and musicians we know our audience love."
The Voice UK will debut early next year.
Holly Willoughby and Reggie Yates will host the singing competition, which sees hopefuls perform for the coaches in blind auditions.
> Jessie J: 'The Voice UK won't laugh at people like X Factor'