Luke Combs, Eric Church, and Darius Rucker were set to headline the popular European country music festival.
The festival will again take place in London, Glasgow and Dublin on 13-15 March near year, and in the two cities in which it debuted this year, Amsterdam and Berlin.
Lyle Lovett, Drake White and Ashley McBryde were among his fellow attractions on C2C's closing London bill.
Other attractions on the main stages at the London event included Carly Pearce, Catherine McGrath and Fairground Saints.
The first day of the multi-city festival's showpiece London event also featured an outstanding performance by Cam and many other highlights.
Frequent UK visitor Underwood will play the five arena shows in June and July.
The seventh edition of Europe's biggest musical festival will also star Lyle Lovett, Drake White, Ashley McBryde and many more.
uDiscover reviews the London edition of C2C 2017, the Country to Country Festival, with major current country stars, revered heritage acts and new names.
Kylie Olsson presents highlights from CTC 2016 & interviews Ashley Campbell, Thomas Rhett, A Thousand Horses, Maddie & Tae at the Big Machine Label hangout!
The Yamaha Music Stage at C2C 2016 at London's The 02 will star hot Nashville acts Ashley Monroe, Striking Matches, Frankie Ballard and more.