[4][5] Former player and family friend Lan Bale recommended the brothers to University of California head tennis coach Peter Wright when they were 12 and 13 years old.

[2] Bale and Thomas Shimada helped to facilitate the change of allegiance, in order for McLachlan to take advantage of the funding and support on offer from the Japan Tennis Association.

[7] McLachlan played his first Grand Slam tournament at the Australian Open, partnering German Jan-Lennard Struff to reach the semifinals after defeating the top-seeded and world No.

In Madrid they beat John Isner and Jack Sock in the first round and Ivan Dodig and Rajeev Ram in the second, before losing to Pierre-Hugues Herbert and Nicolas Mahut in the quarter-finals.

Reunited with Struff at Roland Garros, the pair suffered a surprise defeat at the hands of Marcelo Arévalo and Jamie Cerretani in the first round, losing in three sets.

In his last tournament before the US Open, McLachlan resumed his partnership with Struff at Winston-Salem, but they were knocked out in the first round by eventual runners-up Jamie Cerretani and Leander Paes.

In the year's final major event, he and Struff were the 12th seeds in the men's doubles, but were knocked out in the first round by the Italian pair of Matteo Berrettini and Andreas Seppi.

In the mixed doubles McLachlan resumed his partnership with Makoto Ninomiya, but they lost in the first round to the eventual runners-up, Alicja Rosolska and Nikola Mektić.

The next event for McLachlan was the Davis Cup tie in Osaka against Bosnia/Herzegovina where, reunited with Yasutaka Uchiyama, they beat Tomislav Brkić and Nerman Fatić in straight sets to seal victory for Japan.

[10] A week later he successfully defended his Japan Open crown in Tokyo, but this time with regular partner Jan-Lennard Struff, beating Raven Klaasen and Michael Venus in the final.

From there they headed to Auckland, where they beat Łukasz Kubot and Horacio Zeballos in the first round, Marcus Daniell and Wesley Koolhof in the quarterfinals and the top seeds Oliver Marach and Mate Pavić in the semi-final, requiring two tie-breaks in all three matches.

McLachlan changed partners for the Open 13 in Marseille as Struff didn't attend, teaming up with Matwé Middelkoop to go all the way to the final, where they lost in a match tie-break to Jérémy Chardy and Fabrice Martin.

More first round losses followed over the next three months, the streak reaching eight with his and Struff's exit from Roland-Garros, where they had been seeded 15th, at the hands of eventual runners-up Jérémy Chardy and Fabrice Martin.

He also played mixed doubles at the French Open, teaming up again with his partner from Wimbledon, Eri Hozumi, but they lost in a first round match tie-break to María José Martínez Sánchez and Neal Skupski.

A run of first and second round losses continued for the next month, their last event together for 2019 being in Vienna, where they had to qualify before eventually losing in the quarterfinals to Rajeev Ram and Joe Salisbury, the latter going on to defend the title he had won the previous year with Neal Skupski.

They lost two very close matches, beaten 6–7(4), 6–4, 7–5 by the French pair of Pierre-Hugues Herbert and Nicolas Mahut, and 7–6(5), 7–6(4) by Janko Tipsarević and Viktor Troicki of Serbia.

McLachlan and Bambridge made a winning start to the year in Auckland, taking their first title together by defeating Marcus Daniell and Philipp Oswald in the final.

Ecuador won the tie 3–0 to qualify for the finals in Madrid in November (but which were subsequently postponed), with Japan returning to World Group I, where they are scheduled to eventually play away to Pakistan.

McLachlan teamed up with Raven Klaasen in Cologne, becoming champions in their first tournament together when they defeated French Open title-holders Kevin Krawietz and Andreas Mies in straight sets in the final.

McLachlan rejoined Skugor in Nur-Sultan, losing in the semifinals, before he and Klaasen were upset in the first round of the Paris Masters by Taylor Fritz and Casper Ruud.