Seirawan began playing chess at 12; at 13 he became Washington junior champion. At 19 he won the World Junior Chess Championship. In 1980, he tied for first with Walter Browne in Wijk Aan Zee and was invited by Viktor Korchnoi to be his coach in the 1980/81 Candidate Matches and World Championship match against Anatoly Karpov.
Seirawan was twice a Candidate, four time US Champion, was ranked in the world's top ten and played for ten US Olympiad teams. He retired from tournament play in September 2003.
For twelve years he was the publisher chief editor of the Inside Chess magazine.
In 2001, Seirawan released a plan to reunite the chess world, which at that time had two world champions: Ruslan Ponomariov had gained the title under the auspices of FIDE, while Vladimir Kramnik had beaten Garry Kasparov to take the Einstein title. It called for one match between Ponomariov and Kasparov (the world number one), and another between Kramnik and the winner of the 2002 Einstein tournament in Dortmund (who turned out to be Péter Lékó). The winners of these matches would then play each other to become undisputed World Champion. This plan was signed by all parties on May 6, 2002, in the so-called "Prague Agreement". The Kramnik-Leko match took place (the match was drawn, with Kramnik retaining his title); the Kasparov-Ponomariov match was canceled in 2003, and this particular plan became moot after the September–October 2006 FIDE World Chess Championship 2006 between Kramnik and Veselin Topalov reunited the world championship title .
In the July 2007 FIDE list, Seirawan had an Elo rating of 2634, placing him in the top 100 chess players in the world, and America's number four (behind Hikaru Nakamura, Gata Kamsky and Alexander Onischuk). He played six games in the July 2007 FIDE update.
In 2007, Seirawan unveiled his enhanced chess game called Seirawan chess which he is currently promoting worldwide. The first ever event was a 12 board simultaneous exhibition held March 31, 2007 in Vancouver, Canada.
In July 2011, Seirawan returned from an eight year hiatus to competitive chess, playing in the 2011 US Championship as well as the world team championship in Ningbo, China, where he won a Silver medal for his 4th board. He had significant results, including wins vs. GM J. Polgar and GM Mamedyarov, both active and much higher rated players.