2008-09: Tom Nilsson played for the Hanvikens SK youth club and appeared in five games with AIK's U-16 team – with no points and 4 PMs.
2009-10: Nilsson spent the season with Mora splitting the year between the U-18 team at the Elitserien and Allsvenskan junior levels as well as playing three games at U-20. Scoreless in the three U-20 games, Nilsson played 35 games at the U-18 level and scored 11 goals with 9 assists and had 30 PMs.
2010-11: Nilsson spent the bulk of the season with Mora's U-18 and U-20 teams and made his pro debut with Mora (Allsvenskan – Sweden’s second division) – playing three games in the regular season and ten more in the Kvalserien (relegation playoffs). While his offensive contribution wasn't much of a factor, just one assist in 13 games, his physical, defensive play confirmed much of what scouts saw of him with Team Sweden at the 2011 World U-18 Championships. In six games, he had one assist but at times was Sweden's most noticeable defenseman. In 37 games for Mora's U-20 squad, he scored 2 goals with 6 assists and drew 26 PMs. In 12 contests with Mora U-18, he had 1 goal, 7 assists and 22 PMs. Though not listed among the top 140 European skaters in Central Scouting's final rankings, Nilsson was selected by the Maple Leafs in the 4th round (100th overall) of the 2011 NHL Draft.
2011-12: Nilsson skated in 44 of 52 games for eighth-place Mora IK in Sweden's AllSvenskan (second league). He scored 4 goals with 6 assists and was plus-ten with 45 penalty minutes. Nilsson played in 12 games with Mora's U20 team, including 2 playoff games and had three assists. He represented Sweden in 10 international matches at the U19 and U20 levels but did not play in any world championship tournaments.
2012-13: Nilsson signed a three-year, entry-level contract with the Maple Leafs in March of 2013 following his second season in Allsvenskan with Mora. He played 42 games for Mora and also played for Sweden's silver medal-winning squad at the 2013 World Junior Championship. Nilsson scored 1 goal with 3 assists and was -11 with 18 penalty minutes in Allsvenskan play, Mora finished eighth; missing the league playoffs. Nilsson had 2 assists and was +3 with 4 penalty minutes in six games at the WJC. Sweden lost to the USA, 3-1, in the gold medal game. Nilsson was loaned to Frolunda in Sweden's SHL in April of 2013 and will spend the 2013-14 season with the club.
Nilsson is a throwback, heavy body-checking, defensive defenseman who draws the ire of his opponents with his sometimes borderline legal, antagonistic play. Some scouts see elements of long-time NHL defenseman Ulf Samuelsson in his approach to the game, but he has not yet demonstrated the offensive elements and instincts that Samuelsson had. A right-handed shooting defenseman (somewhat rare among Europeans), Nilsson has a solid shot from the point.
Nilsson will make his Swedish Hockey League (SHL) debut in 2013-14 as a member of Folunda. He is expected to join the Toronto Marlies in 2014-15. He has a contract in place with Frolunda until 2015-16 should the Maple Leafs decide to leave him in Sweden to develop.