In 2013, Muirhead was part of the Scottish team that won the World Junior Curling Championships, the first time Scotland had won the event since 1996, and a silver medal at the 2013 Winter Universiade. In 2014, Thomas and his brother Glen joined Tom Brewster's curling team, and also competed in the 2015 World University Games. Muirhead now competes for Team Smith, led by Kyle Smith. After four weeks of the 2016 season, Smith's team was leading the World Curling Tour. Thomas competed against his brother Glen, winning the match 4–2. In 2016, he was part of the first British team to reach the final of a Grand Slam of Curling bonspiel. Muirhead was in the team that came second at the 2017 European Curling Championships. After finishing in the top eight at the 2017 World Curling Championships, Team Smith qualified for the 2018 Winter Olympics in Pyeongchang, South Korea. Thomas was selected as the third, whilst his brother Glen was chosen as the alternate for the men's curling team, and his sister Eve was chosen to skipper the women's curling team.