He started playing in the chess clubHamburg SK, where he still continues to be a member. As a young chess player he soon became successful, and won the German team championship in the age group U13 in 1992. Two years later he won the German championship in the age group U15, and 1996 both the individual championship in the age group U17 and the team championship in the age group U20. He plays in the German Chess Bundesliga since 1997. In year 1999 he was appointed FIDEInternational Master, and earned the title grandmaster in 2003. He was nominated to the German national team in 2002, due to merits gained in a match with Greece, and in 2004 he represented Germany in the 2004 Chess Olympiad at Calvià. Gustafsson is one of the strongest German chess players, and finished second in the 2004 and 2005 German championships. He is also considered a very strong blitz chess player, winning the German blitz championship in 2001. In 2011 he tied for 1st-3rd with Nigel Short and Francisco Vallejo Pons in the Thailand Open in Pattaya and won the event on tie-break. His handle on the Internet Chess Club is "GodGusti".
His top Elo rating is 2652, recorded in November 2010 until January 2011. He occasionally plays a lot of poker, and has written a book on poker together with Dutch professional poker player Marcel Lüske.