Lowry was the 2007 Irish Amateur Close Champion, defeating Niall Turner 4 & 3 in the final. While still an amateur in May 2009, he won The Irish Open on the European Tour, defeating Robert Rock on the third hole of a sudden death playoff. The win, on his tour début, made him just the third amateur to win on the European Tour, following Danny Lee earlier in the 2009 season, and Pablo Martín in 2007. Lowry shot a 62 to equal the lowest ever by an amateur on the circuit and led from the second round onwards.
Lowry made his professional debut in the 2009–10 UEFA Europa League in an away fixture at Rapid Vienna. On 17 September 2009, Lowry signed a three-month loan deal with Football League Championship side Plymouth Argyle. Lowry made his Plymouth Argyle debut on 19 September 2009, playing 90 minutes, in a 3–1 loss against Newcastle United. He played 13 league games for Plymouth during his loan spell, where he impressed many and was recalled by Villa who required Lowry's services as cover after some injuries to defenders.
The Open Championship: Playing in the final group Sunday for the second straight time in a major championship, made a solid bid for the title, at The Open Championship, with a final-round, 5-under 67. Along with Garcia, finished second to Rory McIlroy by two strokes. With his finish at Royal Liverpool GC, became the only player of the season to claim top-five finishes in the year's first three major championships. He also became the first player to claim top-10 finishes in a season's first three majors since Woods achieved the feat in 2005. His T2 at Royal Liverpool supplanted his previous-best Open Championship finish (in four starts) of T5 in 2011. Rounds of 69-69-68-67 made him the only player in the field to post all four rounds in the 60s.
In June 2015, he became the first SMU Mustang to win the NCAA individual championship, recording a score of 280 (−8) to win by one stroke. In August, he won the U.S. Amateur title, defeating Derek Bard 7 & 6 in the 36-hole final. He became the fifth player to win both the NCAA and U.S. Amateur titles in the same year, joining Jack Nicklaus (1961), Phil Mickelson (1990), Tiger Woods (1996), and Ryan Moore (2004).
Lowry elected to turn professional the week after his Irish Open triumph, meaning that he would miss out on the opportunity to play in the Walker Cup in September 2009. He made his professional début on 28 May at the European Open, where he shot 78 in the first round to end the opening day almost at the back of the field, and went on to miss the cut following a second round 73.
Some modern pros, including Woods, have caught flak for working out too hard and wearing down their bodies. For DeChambeau, the philosophy is the exact opposite: His gym inspiration is to stave off a nagging back injury. That injury — which DeChambeau says stems from a childhood trampoline accident plus the wear of hitting nearly infinite range balls — left him in major pain last season. “Sleeping hurt, everything hurt,” he said. “But it’s pretty cool what you can do to the body by working out. Most people say, ‘okay, I just have to sit down and rest, I’ve gotta take time off,’ but I’ve tried that route and I’ve realized that actually makes you worse.”
Wells Fargo Championship: Made birdie-3 on the first extra hole (No. 18) to defeat Rory McIlroy and D.A. Points at the Wells Fargo Championship for his first TOUR win. Improved to 1-1 in playoffs (lost to Troy Matteson, 2009 Frys.com Open). The playoff was the fifth at the Wells Fargo Championship. At the age of 23 years, 4 months, 23 days, became the third player to make the Wells Fargo Championship his first PGA TOUR win (Anthony Kim in 2008 and McIlroy in 2010). Became the third-youngest winner of the event, behind McIlroy (20 years, 11 months, 28 days) and Kim (22, 10, 15). His win came in his 72nd start on TOUR and was his 16th top-10 finish. Opening-round 66 is the lowest start by a winner of the Wells Fargo Championship. Won in his third start at the Wells Fargo Championship (T6 in 2010 and T16 in 2011).
Hyundai Tournament of Champions: Finished T6 in a Monday-start-Tuesday-finish event, the season-opening, 54-hole Hyundai Tournament of Champions. The event "started" twice during the regularly scheduled first round Friday and later Sunday, but both times PGA TOUR rules staff halted play due to unplayable windy conditions and subsequently voided all scores that had taken place. As the first player off the tee, he ended up hitting three "opening" shots of the season.