Simpson began his coaching career in 1992 as an assistant coach to Björn Kindling and later Jim Koleff at EV Zug in the Swiss elite league National League A. Prior to the 1997-98 season, Simpson was promoted to the head coaching position and guided Zug to the NLA championship in his first year at the helm. Zug had also finished the regular seasonon top of the NLA table. Simpson served another year as Zug head coach and then joined the München Barons of the German top-flight Deutsche Eishockey Liga for the 1999-2000 season and won the DEL title his first year. The following season, he coached the Barons to another finals appearance, where they lost 3 games to 1 to Mannheim. In 2001-02, Simpson led the Barons to the semifinals, where they lost to Kölner Haie. The franchise was relocated to Hamburg in 2002 and renamed the Hamburg Freezers. Simpson coached the Hamburg team in its inaugural season and led the Freezers to a playoff berth. He left Hamburg after the season to return to EV Zug. In 2003-04, he guided EVZ to the NLA playoffs, where they fell short in the quarterfinals, despite having former NHL star Claude Lemieux on the team, who had signed with Zug in February 2004 for the remainder of the season. In 2004-05, Simpson guided Zug to the NLA semifinals but did not manage to get past the ZSC Lions. The following season, Simpson's team was held off by Rapperswil-Jona in the quarterfinals and reached the semis one year later. In his final year at the Zug helm, Simpson coached EVZ to another playoff appearance but did not get past the quarterfinals. Simpson inked a deal with reigning Swiss champs ZSC Lions in 2008. In his two years at ZSC, Simpson guided the Lions to the Champions Hockey League title and the Victoria Cup title in 2009. In the NLA, the Lions dropped out in the playoff quarterfinals both years. During his tenures at EV Zug and ZSC, Simpson was named to the coaching staff of Team Canada for the Spengler-Cup five times and guided the team to the title in 2007. Simpson was named head coach of the Swiss national team prior to the 2010 World Championships and remained in that job until 2014. At the 2010 World Championships, Simpson's team defeated Canada in the preliminary round and made it to the quarterfinals, before falling short to host Germany. In 2011 and 2012, the Swiss team failed to qualify for the quarterfinals at the World Championships. In 2013, Simpson led the Swiss national team to its greatest ever success, a silver medal at the World Championships in Sweden. At the 2014 Olympic Games, Simpson's squad missed the quarterfinals and finished in ninth place. In April 2014, he became the head coach of KHL team Lokomotiv Yaroslavl, but was sacked after nine games. In December 2014 he became the head coach of the Kloten Flyers in the Swiss National League A. In May 2016, after the club had been sold to Hans-Ueli Lehmann and after budget cuts had been announced, Simpson's contract with Kloten was terminated by mutual consent. He was named head coach of Adler Mannheim of the Deutsche Eishockey Liga on May 11, 2016. In the 2016-17 season, he led the team to a second-place finish in the regular season, before falling short to Eisbären Berlin in the playoff quarterfinals. After the final loss, Simpson grabbed the headlines by threatening a TV reporter. He later apologized for the incident. On December 4, 2017, Simpson was relieved of his duties as Mannheim head coach due to the team's poor results. The Adler team was in seventh place, when Simpson was sacked.
