London's 25-year-old O'Donnell was one of four players, alongside China's Chen Zhe, Devon's Sam Baird and Preston's Ian Burns, to come through the first Q School event and earn a place on the main circuit for 2012/13 and 2013/14. The quartet will be in the draw when the new season starts with the Wuxi Classic qualifiers in early June.
O'Donnell beat Australia's Adrian Ridley 4-1 in the final round, going 3-0 up with a top break of 81 before sealing a nervy win in a scrappy fifth frame.
"It was just a relief to win in the end," said the player nicknamed 'The MOD', who qualified for Q School by winning the Snookerbacker Classic. "When you get to the final round you just want to get the job done, it would have been tough to go back to round one.
"I felt really good this morning, and even when I was 2-0 and 3-2 down to Paul Davison (in the penultimate round) I knew that if I got chances I could do it. My form over the past 18 months has been good and I have won a few amateur events which gave me a lot of belief.
"It hasn't sunk in yet, but it has been my dream to play on the main tour since I was 12 years old. It has taken me longer than I had hoped, but I have got a crack at it now for two years. I'm under no false pretences about how tough it will be, but I believe I have a strong all-round game and I am good enough for the tour."
O'Donnell, who is resident pro at the RAC Club in London, added: "I will need to hit the ground running and to improve in every aspect. It's tough to get on the tour and probably twice as tough to stay on. I have practised with Martin Gould for 11 years and what he has done is an inspiration. He went from nowhere to being a top 16 player in four or five years and that shows it can be done."
Baird achieved the extraordinary feat of winning all five Q School matches without conceding a frame. He finished off with a 4-0 win over Nick Jennings, with top breaks of 56 and 62. Baird dropped off the main tour at the end of last season despite a fine run to the last 32 of the Welsh Open, where he came within two balls of beating Mark Selby 4-2 but eventually lost 4-3.
"That was a big disappointment and it took me a few weeks to get over it," said 23-year-old Baird after bouncing straight back on to the tour. "I have bossed games like that before and I just have to get used to winning at the venues. I did better than I thought I would last season but still didn't manage to stay on. It's good to have two years now, but you still have to do well in the first year.
"I have played well this week and got off to a good start in every match. I didn't mind how I got through as long as I kept winning."
Chen earned a place on the tour for the first time by beating Jordan Brown 4-1. He will now join the growing army of Chinese players on the circuit. Chen, age 19 from Shanxi, is based in Romford and has sharpened his game by practising with World Champion Ronnie O'Sullivan.
Burns, age 27, was the third player to secure a tour place for the first time as he edged out stalwart Rod Lawler 4-3. Former International Open finalist Lawler came from 3-1 down to 3-3 and led 43-0 in the decider, only for Burns to make a superb 73 clearance.
Event two starts on Saturday.
Ball by ball scoring and results from tournaments