On 15 January 2014, Johansen sealed a move to Scottish Premiership club Celtic for a transfer fee of £2 million. Johansen signed a three-and-a-half-year contract with the club, and became the fourth Norwegian to play for Celtic following Harald Brattbakk, Vidar Riseth and Thomas Rogne. He was given the number 25 shirt, the same number worn in previous years by Ľubomír Moravčík and Shunsuke Nakamura.
Johansen made his debut for Celtic in the 4–0 victory against Hibernian on 26 January 2014 when he played the last five minutes as a substitute. He scored his first goal for Celtic on 22 March 2014 in a home league match against St Mirren, opening the scoring in a 3–0 win with a header.