Roche, who moves from Tinkoff-Saxo, was announced as one of five new riders for Sky on Tuesday as they look to build a strong team for 2015's Grand Tours.
Along with the 30-year-old Irishman, the team have also signed Andrew Fenn, Lars Petter Nordhaug, Wout Poels and the highly-rated Leopold Konig.
Konig joins from Team NetApp-Endura having impressed on his way to a seventh-place finish at the Tour de France.
Roche, who has appeared in 13 Grand Tours, revealed the opportunity to work alongside Sky's team prinicipal Dave Brailsford was a major factor in his decision.
"It's a great honour to sign for Team Sky and I have the opportunity to ride with some of the best riders in the world," he told the team's official website. "I feel that I am still developing as a rider so now's the perfect time to join Team Sky and to continue my upwards path.
"I'm confident that under the guidance of Dave Brailsford and the team, I'll continue to improve."
Having supported former team-mate Alberto Contador on his Grand Tour victories, Roche is looking forward to aiding Chris Froome following his switch.
"From what I understand I will be doing bit of everything," he told Sky Sports News. "The main goal is to win the Tour de France with Chris Froome.
"That is something I want to play a part in and am really excited for.
"On the other races I might have a chance [to win], that's what I enjoyed about the project, there are multiple faces to it."