The announcement was made at the Star Sports studios in the KKR-Star Sports show called Knight Club.
Present on the occasion were KKRs MD and CEO, Venky Mysore, and Karthik himself.
Karthik said he was looking forward to lead a side having a combination of youth and experience.
"It is an honour to represent Kolkata Knight Riders, one of the most successful franchises in the IPL and I look forward to this new challenge. I am excited about the squad that has been assembled, which has a great combination of experience and youth," said Karthik.
Regarding the team's vice-captain, he said, "Robin has been an integral part of KKR since 2014 and played a crucial role in KKR winning the championship. We are fortunate to have both Dinesh & Robin in leadership roles for KKR."
KKR play their opening game on April 8 at the Eden Gardens.