On July 3, 2020, it was revealed that Kai was preparing to make his solo debut sometime later in the year. He made his solo debut on November 30 with his self-titled mini album.
He graduated from School of Performing Arts Seoul (SOPA) in February 2012.
On April 1, 2016, local media outlet Dispatch reported that he and Krystal of f(x) were dating and it was confirmed by SM Entertainment on the same day. In June, 2017, SM reported that the couple have broken up due to busy schedules of both sides.
On December 31, 2018, rumors of a possible relationship between he and Jennie of BLACKPINK began to take off when the same local media outlet of the last time posted pictures of the two together on a date, with the information that they also had spent time together in Paris back in October. On January 1, 2019, SM Entertainment confirmed the pair were dating and gave the statement, "Kai and Jennie have become fond of each other". Later that day, YG Entertainment also confirmed the news. On January 25, SM Entertainment revealed that the couple had broken up, but did not reveal the reason for it.