Antonius was mentored by poker pro Marcel Lüske as a member of Luske's "Circle of Outlaws"[2] and later advised by Jennifer Harman.

[8][9][10] In September 2005 he made the European Poker Tour (EPT) Main Event final table, finishing 3rd in Barcelona.

[11] The next month, Antonius won the EPT event in Baden bei Wien, taking home the €288,180 first prize when in the final hand his 8♠ 4♥ beat Gunnar Østebrød's Q♥ 9♣ on a board of 4♠ 7♠ 8♥ 3♣ 7♣.

In December 2005 he finished the year 2nd in the WPT Five Diamond World Poker Classic in Las Vegas, Nevada, winning $1,046,470.

[13] In the 2007 World Series of Poker, Antonius entered numerous tournaments but he only cashed in the World Championship of Pot Limit Omaha event, placing third and winning $311,394, making that his ninth WSOP cash and increasing his WSOP earnings to a total of $569,964.

In his first appearance, he finished as runner up, losing out to fellow poker professional Jennifer Harman,[15] but his next attempt saw him defeat Brad Booth in heads-up play to take the victory.

[17] Antonius was not able to enter the 2009 WSOP Main Event, as he was turned away when attempting to register along with hundreds of others due to a capacity field.

[18] He also plays in some of the highest profile online tournaments, and in September 2008, he finished 2nd in the Full Tilt Poker $25,000 buy-in Heads-Up Pot Limit Omaha Championship, winning $320,000.

[21] In March 2018, Antonius earned his largest live cash with a runner-up finish in the Super High Roller Bowl in Macau.

[23] In April 2024, Antonius won the €100,000 Super High Roller title at the PokerStars European Poker Tour in Monte Carlo, earning €1,967,440 after a heads-up victory against Christoph Vogelsang.

[4] In November 2024, Antonius claimed the $200,000 NLH Invitational title at the Triton Poker Series in Monte Carlo, winning $5,130,000 following a heads-up match against Vladimir Korzinin.

Sammy called Patrik's all-in raise instantly and the two agreed to run the turn and river four times.

Antonius has since lost a pot of almost $600,000 to Tom Dwan on an episode of the Poker After Dark high-stakes cash game.

[31][32] Antonius was born in Helsinki, grew up in Hakunila, Vantaa, and he lived in Las Vegas, U.S, before he moved to Monte Carlo, Monaco, in 2008.