The New Zealand rep, who began in a share of the lead with Auckland amateurs Tae Koh and Sam An at 10-under par, shot a tumultuous three-under par 69 in the fine conditions to secure his maiden senior national title by two shots.
Australian Amateur Champion Koh (71) finished runner-up while Takaka golfer Blair Riordan (70) and An (73), who claimed the Te Mana A Toi trophy for the tournament low round, finished in a share of third place.
But today was all about Toomey. He became only the fifth golfer from the Waikato to win the St Andrews Salver following Ted McDougall (Tokoroa), Brad Shilton (Te Awamutu), Colin Taylor (Hamilton) and James Gill (Hamilton) and the first champion from the province for seven years.
The 21-year-old from the Riverside Golf Club, who held the third round lead two years ago in the same championship, was proud that he showed his renewed maturity to close out the title.
"I am just absolutely stoked to no longer be a bridesmaid and to win this after one of my best friends in Cam [Jones] last year makes it really special," said Toomey.
"I have had that many second and third places I have been wondering when it would be my turn and to open it up at the New Zealand Stroke Play is unbelievable."
Toomey got off to the worst possible start when he made a double bogey on the opening par five when he hit his approach with a three wood out of bounds.
"I made a four foot putt there for double and I took some positives from that into the next few holes."
Toomey brushed off the bad start and made four birdies in a row in what was a tournament-defining stretch where he earned a three shot lead heading into the back nine.
He scrambled hard on the 10th to make par to An's birdie then on the par four 11th he blocked his tee shot right and had to chip out backwards. The result was a double bogey and all of a sudden An and Toomey were tied at the top.
"I seemed to keep giving the guys a chance but overall I am really pleased with my performance. The holes that followed the bad ones were spectacular."
Like he did on the front nine, when he looked vulnerable Toomey came back harder.
He hit a superb approach to the par four 12th from 128m and made the 15 foot putt to get back into the lead and from there he never looked back.
"It was really gutsy to make birdie on 12 and that gave me the belief again. Putts seemed to drop at the right moment and I am stoked."
Toomey made a clutch birdie on the par 3 16th and then scrambled from poor positions on 17 and 18 to secure the long awaited win.
He said it was nice to add his name to the list of legends on the St Andrews Salver that includes the likes of McDougall, Ross Murray, Marcus Wheelhouse, Gareth Paddison and Tim Wilkinson.
"There are many legends on there, and don't forget that Brad Kendall and Cameron Jones are on there too [laughs]. I am looking forward to getting my hands on it and having a look who I have followed."
He is hopeful that this performance is noted by the selectors as he looks to make the New Zealand team to compete in the Eisenhower Trophy in Japan.
"It is good timing with the Eisenhower coming up "“ it is the biggest team's championship in the world and naturally I want to play it "“ but I don't want to get too caught up in whether I am going to get selected or not."
First things first and that would be about celebrating his success this week at Bridge Pa. He is looking forward to returning to the Riverside Golf Club with the prized silverware.
"I hope it gets in there somewhere in their hearts. I really look forward to playing pennants next week and catching up with the guys. It is not just Riverside but St Andrews and Ngaruawahia have played a big part in my development."
Minami Katsu is the first Japanese golfer to win the New Zealand Stroke Play Championship in more than 100 years.
The 15-year-old, who began the final round with a six shot lead, completed a superb performance when she carded a four-under par 70 at the Hastings Golf Club today to win by seven shots and set a record for scoring in the event.
Auckland golfer Munchin Keh (70) chipped in on the final hole for eagle to claim second place from Japan's Haruka Morita (72) who three-putted the last for par.
But this week was all about the performance of Katsu. The New Zealand Stroke Play of 2014 will be remembered as the time when the young Japanese golfer made history.
The Mellsop Cup, which dates back to 1911 and has been won by many of New Zealand's best, has never been won by a Japanese player until now.
"It is a huge honour to be the champion in New Zealand," said Katsu through a translator. "I am very happy."
Katsu made five birdies and a bogey in her round today and never looked like relinquishing the lead. She signed for rounds of 69, 70, 68 and 70 for an incredible 19-under par total for a record total.
In recent time New Zealand's Lydia Ko was seven-under par when she won the NZ Stroke Play in 2011 at the Russely Golf Club and the last time Hastings staged the championship Emily Perry and Ko finished on 12-under par before Perry prevailed in the playoff.
"I tried to treat it like it was the first day of the championship and that helped me to stay calm. I am so happy to have that record.
Her best memories from New Zealand were making a long putt for birdie in the third round and the food she has eaten every day in the Hastings Golf Club.
"I love the bacon and egg quiche... and the summer fruit. I love the food here."
She was one of six Japanese golfers (three men and three women) in New Zealand to compete in the championship to further develop the international experience of the players in the National Team.
It is believed to be the first time that Japanese golfers have contested the New Zealand Stroke Play Championship.
The diminutive golfer, who is ranked 142 in the Official World Golf Rankings and the Japan No.2, said this win would help her self belief as she prepared for the Queen Sirikit Cup.
"Winning this championship will give me a lot of confidence. I will continue to practice hard and look to improve for the big tournaments coming later in the year."