In his first major poker tournament, Seidel was runner-up in the 1988 World Series of Poker Main Event to Johnny Chan. This final hand was featured in the 1998 movie Rounders. Seidel made the WSOP Main Event final table again in 1999, finishing in fourth place in the event won by Noel Furlong.
Seidel won his first WSOP bracelet in 1992 and won his eighth and most recent bracelet in 2007 Seidel has won bracelets in five different games, including Hold'em, Omaha, and Deuce to Seven Draw. Only five players in the history of the WSOP have won more bracelets than Seidel: Phil Hellmuth, Doyle Brunson, Johnny Chan, Johnny Moss, and Phil Ivey.
In January 2007, Seidel finished in second place in the Aussie Millions $100,000 event and took home $550,000(AUD), beaten by Erick Lindgren in Heads-Up play when he moved all-in with KJ of hearts on a two-heart flop and Lindgren called with a pair of aces and his 7 kicker became an eventual straight.
In January 2008, Seidel finished in second place in the Aussie Millions $10,000 main event and won $1,000,000(AUD).
In March 2010, Seidel finished in second place in the National Heads-Up Poker Championship and collected $250,000 after a 2–1 loss to Annie Duke in the final.
In August 2011, Seidel finished runner-up to David Rheem in the $20,000 buy-in 6-Max No Limit Hold'em tournament at the inaugural Epic Poker League for $604,330, which brought his earnings for 2011 to over $6.2 million.
In May 2015, Seidel won the 2015 European Poker Tour Grand Final €100,000 Super High Roller for €2,015,000.
As of 2016, his total live tournament winnings exceed $34,000,000, of which $5,320,192 have been won at the WSOP. His 101 WSOP cashes rank him second all-time. Erik has won over $5,000,000 in poker earnings in years 2011, 2015, and 2016. As of January 2017, while many players have made over $5 million in a year no other player has done this more than once. In January 2016, Seidel was ranked #28 on the Global Poker Index. (He was #1 for a total of 15 weeks in 2011).