Adamek made his professional boxing debut on March 13, 1999, at Bowler's Arenac in Manchester against Israel Khumalo. He won by TKO in first round.

Winning the light heavyweight title

Adamek won the vacant WBC light heavyweight title defeating Paul "Firepower" Briggs by majority decision on 21 May 2005. The fight was described by some as one of the most brutal in recent memory, as Briggs suffered a large cut above his left eye early in the fight and Adamek bled profusely from his nose for much of the fight(broken), as well. Adamek tended to be the aggressor and win the fight.

On 15 October 2005, he defended his title against German boxer Thomas Ulrich by knockout in Round 6.

He then defended his title in a rematch with Paul Briggs in 2006, again winning by majority decision. After the fight Jim Lampley said (Adamek vs Briggs I and II) was the best combined 24 rounds he has ever seen.

Adamek vs. Dawson

Undefeated Adamek with 31-0 (21 KO) lost his first fight by unanimous decision to Chad Dawson on 3 February 2007. During that fight, Adamek was knocked down in the seventh round; this was only the second time in his career he has been knocked down (upon slow-motion replay on Showtime, Adamek tripped on Dawson's foot after the body shot). Adamek knocked Dawson down late in the fight but could not knock him out, and was already too far behind on points to get the decision. Immediately following the loss to Dawson, Adamek decided to move up in the cruiserweight division.

Moving up to cruiserweight

After losing to Dawson, Adamek moved up to cruiserweight to beat Luis Andres Pineda by technical knockout in round 7 to become the IBO cruiserweight champion. He successfully defended his title against Josip Jalusic on 29 December 2007 in Germany.

Adamek vs. Bell

On April 19, 2008 in Poland, Adamek fought former undisputed cruiserweight champion O'Neil Bell in an IBF cruiserweight title eliminator. Adamek floored Bell in round one and had good success by outboxing Bell. Bell opted not to come out for round eight, citing that he felt dizzy and ill.

Winning the cruiserweight title

In December 2008 he fought the then reigning champion Steve Cunningham at the Prudential Center in Newark, N.J. Knocking a game Cunningham down three times, he won the IBF Cruiserwight championship and the vacant Ring Magazine Cruiserweight Championship in a bout many thought was the fight of the year.

Adamek successfully defended his title against Johnathon Banks on 27 February 2009, at the Prudential Center in Newark. He won with a brutal TKO in the 8th Round. He then went on to defeat Bobby Gunn before a large crowd at the Prudential Center on July 11, 2009, with the referee stopping the bout at the ring physician's advice between rounds four and five.

He vacated the IBF Cruiserwight championship on October 18, 2009. Choosing to move up to the Heavyweight division.

Heavyweight

On October 24, 2009 in Łódź, Poland, Adamek defeated Andrew Golota by TKO in the fifth round to win the IBF International Heavyweight Title. It was the biggest live broadcast in the history of Polish internet.

Then, on February 7th 2010 in Newark's Prudential Center he defeated Jason Estrada by unanimous decision after 12 rounds.

In consequence a fight with Chris Arreola is scheduled for April 24th, 2010.