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.
At the PGA Championship, Fowler carded 74-69-75-68 to finish with a six-over par total of 286, in a tie for 51st place. Early on the third day Fowler rocketed up the leaderboard with three birdies in the first five holes only to falter later in the round with two triple bogeys, effectively ending his hopes of a first major championship and PGA Tour win.
Lowry made his Leyton Orient debut, playing as a left-back position, in the opening game of the season, which saw Leyton Orient lost 2–1 to Chesterfield. Since his debut, Lowry established himself in the left-back position in the first half of the season despite being sidelined with suspension and fitness concern that saw him out for two matches. Following his return to the first team, Lowry played in the central-defense between December and March until he dropped from the first team throughout March. Lowry went on to make his first team return throughout 2014–15 season, making thirty-four appearance in his first season at Leyton Orient.
DeChambeau made his PGA Tour debut as an amateur in June 2015 at the FedEx St. Jude Classic near Memphis, Tennessee, and finished in 45th place. He played in his first major championship at the U.S. Open at Chambers Bay, but missed the cut by four strokes. DeChambeau was unable to defend his NCAA title in 2016 after the SMU athletic department was handed a postseason ban by the NCAA. He decided to forgo his senior season to play in a number of events before turning professional. At the 2015 Australian Masters in November, DeChambeau was runner-up with John Senden and Andrew Evans, two shots behind the winner Peter Senior. He was the low amateur at the Masters in 2016 and tied for 21st place.
On 23 November 2011, Lowry was again loaned out to play in the Championship, this time to Millwall until 3 January 2012. He followed Aston Villa team-mate Nathan Baker who also signed on loan for Millwall two days earlier. Lowry made his Millwall debut three days later, where he played 90 minutes, in a 0–0 draw against Crystal Palace. His impressive display at Millwall soon earned a loan extension. Weeks later on 13 January 2012, Lowry was sent-off in the 22nd minutes after stamping on Nikola Žigić, which saw Millwall lose 6–0. Three years on after signing for Birmingham City, Lowry stated, quoting: "Whatever club I play for I fully commit to that club at the time. I play with my heart on my sleeve. Sometimes in the past I have gone overboard but I was a younger player then, I have learned a lot from these types of experiences. But I am an aggressive player, that’s the way I like to play and I can’t change the way I play. I will use my experience now and be a bit more clever."'
After Lowry's loan spell at Leeds was coming to an end, on 11 May he signed a new two-year contract extension at Aston Villa. It was a remarkable few days for Lowry, he was promoted with Leeds, received a call up to Australia's World Cup Squad and on the same day he signed a new two-year deal with Villa. Despite signing a contract with the club, Leeds United was considering re-signing him for the second time ahead of the 2010–11 season, but never happened.
World Golf Championships-HSBC Champions: Came to the 72nd hole in need of a birdie to get into a playoff with Tim Clark and Bubba Watson at the World Golf Championships-HSBC Champions. Hit a 5-wood from the fairway that came up short and went in the water on the par-5. Made par after taking a penalty and finished T3 after a final-round 70 at Sheshan International GC in Shanghai.
Deutsche Bank Championship: Shot a final-round 3-under 68 to come from one shot back and defeat third-round leader Henrik Stenson at the Deutsche Bank Championship, good for his third career PGA TOUR victory. Earned the win at age 26 years, 8 months, 25 days in his 150th career start. Collected 2,000 points and moved from No. 22 to No. 3 in the FedExCup standings. Has come from behind to win all three of his PGA TOUR events, with his first two wins via playoffs (2012 Wells Fargo Championship and 2015 PLAYERS Championship). Became the sixth consecutive come-from-behind winner at TPC Boston.
What this looks like to the naked eye is a DeChambeau who is visibly larger than he was two months ago, when he first teased the idea of a bigger, stronger self. He was under 200 pounds then — now he’s 222. “I’m going to become like a gymnast. I watch online, on Instagram, these gymnast influencers, and that’s where I want to get.” It’s a step in the right direction, but 222 is not nearly big enough. DeChambeau has a Hulk-like vision for his future.
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 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.
U.S. Open: Playing alongside eventual-champion Martin Kaymer in the final pairing Sunday, followed up his career-best round (3-under 67) in a U.S. Open with a final-round, 2-over 72 to remain T2 (the sixth runner-up finish of his career). It was his best performance in six U.S. Open starts (previous-best finish was a T10 in 2013). It was also his top major championship showing among his 18 starts (previous-best finishes were T5s at the 2011 Open Championship and the 2014 Masters). His pairing with the 29-year-old Kaymer was just the third final grouping at the U.S. Open since 1965 with two players in their 20s. The others were John Mahaffey (28) and Jerry Pate (22) in 1976 and Woods (26) and Sergio Garcia (22) in 2002.
After a tie for fifth at the Masters in April, Fowler had his best finish of 2014 at the U.S. Open at Pinehurst No. 2 in North Carolina. Fowler was runner-up with Erik Compton at −1, best finishes for both at a major, but they were eight strokes behind champion Martin Kaymer. Fowler had another second-place finish, at the Open Championship at Royal Liverpool Golf Club in Hoylake, England. He began the final round six strokes behind Rory McIlroy and finished the day tied for second with Sergio García at −15, two strokes behind McIlroy. At the next major in August, the PGA Championship, Fowler, Phil Mickelson, Henrik Stenson, and McIlroy battled for the title on a rain-soaked Valhalla Golf Club, near Louisville. Despite holding the lead for a good portion of the day, Fowler tied for third. He was only the third player, along with Jack Nicklaus and Tiger Woods, to have finished in the top 5 in all four majors in one calendar year, but the first not to win (Jordan Spieth became the fourth player in 2015). Fowler had 10 top-10 finishes during the 2013–14 season. His 8th-place finish at The Tour Championship moved him to 10th in the world golf rankings.
In September, he signed a clothing deal with Puma. In the same month, he was also chosen as a captain's pick for the U.S. Ryder Cup team. At age 21 years and 9 months when the matches began, Fowler became the youngest U.S. Ryder Cup player of all time, and only European Sergio García was younger when he made his Ryder Cup debut in 1999. Fowler forfeited a hole during foursomes competition on the first match day because of a rules violation, by taking a permissible free drop from muddy conditions in an improper location, a mistake U.S. captain Corey Pavin attributed to Fowler's inexperience. On the final day of the competition in his singles match against Edoardo Molinari, Fowler birdied the last 4 holes to halve the match after having been 4 down after 12 holes.
Lowry started for Leeds in the Football League Trophy Northern Area Final, second leg game against Carlisle United, in which the game was lost with Lowry missing the decisive penalty in sudden death in the penalty shootout. After the game it appeared as though Lowry was attacked by a set of Carlisle supporters who had invaded the pitch. After starting every game for Leeds Lowry was dropped from the Leeds squad for the match against Brentford after suffering an injury, before returning to Villa when his loan spell ended. On 25 March 2010 Lowry re-signed for Leeds for a second loan spell, with his loan lasting until the end of the season. Lowry started at left back for Leeds against Norwich City on his return to the club, a match Leeds went on to lose 1–0 in injury time. Lowry didn't overley impress the Leeds fans in his loan spell at Leeds, with him being mostly played out of position at Left back for the entire spell, he was substituted for Jonathan Howson in the final game of the season against Bristol Rovers with 1–0 down at the time, but his loan spell ended on a high as Leeds were promoted in 2nd place after scoring two goals to go on and beat Bristol Rovers and secure promotion to The Championship.
The Barclays: Held a one-stroke lead over Patrick Reed after 54 holes at The Barclays in the FedExCup Playoffs, before a double bogey-birdie-bogey finish on Nos. 16-18 resulted in a T7 at 6-under 278 with Jason Kokrak and Ryan Moore. Fowler went bogey free at Bethpage Black from the 10th hole in round one until the 11th hole in the final round, a span of 55 holes. His 55-consecutive holes without a bogey became a personal best on the PGA TOUR, besting 53 from the 2010 Memorial Tournament. This streak also marked the longest recorded in Barclays history since hole information began in 1983. Ian Poulter had the longest with 45 in 2010. The finish marked his third top-10 showing in his last four starts in the event (T9/2013, T9/2014).
Fowler has three tattoos. One is a block "G" near his left elbow in honor of Georgia Veach, the daughter of a Seattle pastor and friend. Georgia was diagnosed with lissencephaly. Fowler got the tattoo just before the 2015 Presidents Cup. The second is from January 2016 and contains the name Yutaka Tanaka (Rickie's grandfather) in Japanese script on his left biceps. The third tattoo came just weeks after playing at the 2016 Summer Olympics and is of the Olympic symbols.
Lowry received his first call-up to the full Australia squad for a friendly against the Netherlands in Sydney and the Asian Cup qualifier against Oman in Melbourne in October. He did not play in either match. On 11 May 2010 he was selected as part of Pim Verbeek's 30-man provisional squad for the 2010 World Cup, and travelled to South Africa, but was not included in the final 23-man World Cup squad. Lowry was named in Han Berger's 18-man squad for an August 2010 friendly against Slovenia, but he did not appear in the match.