Hunter turned professional in 1995. His first ranking tournament victory was the Regal Welsh Open which he won in 1998, defeating John Higgins in the final. He was named the Snooker Writers Association's Young Player of the Year for that year.
In the 2001 Benson & Hedges Masters, Hunter beat Stephen Hendry 6-3 in the semi-final before recovering from a 7-3 deficit against Fergal O'Brien to win the final 10-9. He won the same tournament again in 2002 and 2004 by the same scoreline, having trailed 5-0 and 7-2 respectively.
He made further ranking victories that year, winning the British Open and the Regal Welsh for a second time, but was diagnosed with testicular cancer and had to have a cyst removed. He continued to rise through the rankings, reaching the top eight for the first time in the 2003 rankings, and the top 4 in the 2004 rankings. He reached that year's World Championship semi-final, losing to Ken Doherty. Hunter had been 15-9 in front before losing 17-16. That is the only time he has reached the semi-finals of the game's most prestigious event.
On April 6, 2005, Hunter announced that he was suffering from colon cancer. A spokesman for the World Snooker Association said at the time: "Paul will undergo treatment to cure himself of this illness. He would like to reassure his fans and supporters that, as with his snooker career, he is tenacious and positive in his fight against the disease."
He returned to the circuit for the start of the following season, but lost to Rory McLeod in the opening round of the Grand Prix tournament, having only returned to practice 2 weeks earlier, and not confirming his participation until 3 days before the match.
Hunter has been receiving chemotherapy for his illness and has been struggling to find form since beginning treatment. He dropped out of the World's top 32 in the rankings after losing 10-5 to Neil Robertson at the World Championship. He was drawn to play both sessions of his first round match on the same day and was losing 7-2 at the end of the first session. He drew the evening session 3-3, but it seemed his opponent was struggling as he closed on the winning line, and the BBC commentators felt he had been unlucky in two of the frames he lost.
It is believed that Hunter's treatment has been unsuccessful so far and that he is often in pain. A third course of chemotherapy in spring 2006, over 16 weeks, tried to stop the cancer from spreading.
Hunter and wife Lyndsey Fell married in the summer of 2004 and on 26 December 2005, Lyndsey gave birth to their first child, daughter Evie Rose, who weighed 8 lbs, 2 oz.
In his post match interview following his first Masters title win, Hunter caused a media sensation by admitting he resorted to "Plan B" with Lyndsey, then his girlfriend, during the interval while 6-2 down. The 'B' in "Plan B" purportedly refers to the word "bonk", a British slang term for sexual intercourse. Hunter and Fell retired to their hotel room and he recalls "Sex was the last thing on my mind. I just wasn't in the mood. But I had to do something to break the tension. It was a quick session - around 10 minutes or so - but I felt great afterwards. She jumped in the bath, I had a kip and then played like a dream. I reeled off four centuries in six frames. I won easily."
Hunter died of cancer in 2006. His fellow professionals had agreed to have his ranking frozen at 34 in order to take a year off from competitive play.