Lowry started the 2018-19 season with partial status after finishing 140th in the FedEx Cup. He moved into a share of the 36-hole lead at the 2019 Open Championship at Royal Portrush, after successive opening rounds of 67. He was tied at eight under with J. B. Holmes. Lowry then shot a 63 for a new course record to lead by four strokes at the end of the third round. He won the tournament by six shots ahead of Tommy Fleetwood.
PGA Championship: With his T5 finish at the PGA Championship, finishing three strokes behind champion Justin Thomas, continued to be a top-five machine in major championships, recording his seventh such finish in 32 starts. Made a furious Sunday rally, with six birdies, including four in a row on Nos 12-15, but pars on The Green Mile (Nos. 16-18) left him a few short of his friend, Justin Thomas.
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.
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."'
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.