In the summer of 2005 Koenig crossed the Atlantic to join the Newcastle Vipers for their first season in the UK's Elite Ice Hockey League. The season was a huge success for the Vipers as they secured second place in the league and a 2–1 victory over the Sheffield Steelers in the end of season playoff final.^{[citation needed]}

The victory in the playoff final proved to be Koenig's swansong for the Vipers and after the season he transferred to the Coventry Blaze. In the 2005–06 season the Blaze had failed to reproduce similar results of the previous year when they had achieved a "grand slam" of the major UK Ice Hockey honours, and the signing of Koenig was a part of the rebuilding process. 2006–07 was a good season for the Blaze, they won the Elite League and the Challenge Cup, were runners up to the Cardiff Devils in the British Knockout Cup and reached the playoffs semifinals. The playoff semi final, again against Cardiff, was a difficult time for Koenig as before and after the games he flew back over the Atlantic to visit his sick father who was hospitalized.^{[citation needed]}

Koenig continued with the Blaze for the 2007–08 season, but moved to mainland Europe for the 2008–09 term, signing with Rødovre IK of the Danish league and joined on 18 August 2009 to Dragons de Rouen. In July 2010 he signed a one-year deal with the Storhamar Dragons of Hamar, Norway.^{[citation needed]}

On 20 January 2016, Koening signed a contract for the rest of the season with the Dundee Stars of the UK Elite Ice Hockey League.^{[citation needed]}

• Trevor Koenig career statistics at The Internet Hockey Database