Madsen began playing poker at college and won a no limit Texas hold ’em event at the 2006 World Series of Poker. At the age of 21 years and five weeks, he was about six weeks younger than the previous record holder, Eric Froehlich, who won his first WSOP bracelet in 2005. Madsen’s victory earned him $660,948. At that time he was the youngest World Series of Poker winner in history until Steve Billirakis became the youngest at the age of 21 years 11 days the following year. Later in 2007, Annette Obrestad broke that record with her win in the Main Event of the inaugural World Series of Poker Europe on the day before her 19th birthday. Obrestad’s record cannot be broken in the Las Vegas WSOP because Nevada gaming law mandates a minimum age of 21.
Less than two weeks prior to his victory, Madsen finished third in the $2,000 Omaha high-low split event, winning $97,552. Just six days after his first victory, Madsen won his second WSOP title, and $643,381, in the $5,000 no limit hold ’em shorthanded event. A few days later he finished third in the $1000 Seven-card stud high low split event, earning $65,971, adding up to an unprecedented four top 3 finishes, in four different poker variants, in his first year at the WSOP. His showing prompted Full Tilt Poker to bring him in as a sponsored pro.
In 2007, Madsen cashed in his first WPT event, finishing eighth at the Bay 101 Shooting Star Championship.
On February 5, 2010 Madsen won the $3,500 buy-in Championship Event at the Borgata Winter Open 2010 in Atlantic City, NJ winning $625,006.