Wells edged out Michael Wasley 4-3 in a tense final round battle in Sheffield to earn a main tour place for the next two seasons.
Talented Welshman Wells, age 23, suffered a nightmare 2011/12 season, losing a series of matches and developing snooker's version of the 'yips', which led to his relegation from the pro circuit. But he has overcome that problem and is now looking ahead to a fresh start having regained his tour place.
He led 2-0 tonight with a high break of 71 before Wasley battled back to 3-3 with a top run of 75. Both players had chances in the deciding frame, Wasley crucially running out of position at 33-14 with three reds left. Wells later laid a snooker on the last red, and from the chance that followed cleared to the brown, which proved enough.
"It was unbelievable, I've never felt emotion like it," said Neath's Wells, who came within a frame of qualifying for the Crucible on his debut season in 2009. "It's a different type of pressure to what I have been through before and it would have been very tough to lose in the last round and have to play in the last Q School event. But I'm really pleased with how I held myself together tonight.
"Last season was the worst of my career. Around January I was on the verge of packing the game up because I couldn't hit the cue ball. I was scared to hit the ball and couldn't release the cue. I lost to Craig Steadman in a PTC event and he actually said he felt sorry for me.
"Then I went to see coach Del Hill, and he and Mark Fenton have helped me turn it around. Something clicked and everything started coming back to me. I can look forward to next season now and feel as if I am playing well again.
"In the past I have driven myself insane and there was no way I could go on like that. I still want to be a top player, but above all I just want to enjoy the game now."
Wells is now free to run the Sheffield Half Marathon on Sunday to help raise money for the Paul Hunter Foundation and admits he might have pulled out if he had lost tonight. "I could have been playing in Q School event three on Sunday!" he added. "Now I can enjoy the run and hopefully raise some money."
O'Sullivan earned a place on the main tour for the first time with an impressive 4-1 win over Ryan Causton, highlighted by a break of 89 in the third frame.
The 18-year-old from Stepney Green in East London practises with Martin Gould and Anthony Hamilton and can't wait to compete on the pro circuit.
"It's weird, I'm almost speechless," he said. "I knew I had a good chance this week because I've been playing well in practice, and the hard work has paid off.
"Turning pro is what I have wanted to do since I started playing snooker when I was nine. My goal now will be to keep my place on the tour and then try to move up."
O'Sullivan is not related to his namesake Ronnie, but admits the four-time World Champion is his favourite player. "It would be amazing to play him on the tour. I nearly did so in a PTC event but I lost in the round before. I have played a few of the top pros in PTCs so I have got some good experience."
Wellingborough's 25-year-old O'Neill, who was last on the tour in 2010/11, earned his place with a 4-2 defeat of Scott Donaldson, his top break 65.
Yorkshire's 40-year-old Davison, who has played on the tour several times, beat Gareth Allen 4-2 with a top run of 45.
The third and last Q School event starts on Friday, with four more places available.
Ball by ball scoring and results from tournaments