The 25-year-old Pole was the reigning world road race champion at the time of the signing, but was unable to defend his title in Richmond, Virginia.
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Kwiatkowski is the seventh signing announced by Team Sky so far this year. Earlier this week, Spaniards Mikel Landa and Beñat Intxuasti joined the British team from Astana and Movistar, respectively, and Danny Van Poppel arrived from Trek Factory Racing.
Team Sky has also signed British riders Alex Peters and Tao Geoghegan Hart, the latter as a stagiare, as well as Michal Golas and Gianni Moscon.
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Sky team principal David Brailsford said: “Michal has performed fantastically well over the past couple of years. We have been following his career for a long time. We have attempted to sign him on two previous occasions and weren’t going to miss out this time around.
“Team Sky can help him progress and develop both his one-day racing and stage racing.”
Kwiatkowski said: “Sir Dave Brailsford believes in my ability, which gives me great confidence for next season.
“The team’s marginal gains philosophy really fits my approach to cycling and I have great respect for what this team has achieved in such a short time.”