Kubler's career highlight came at the 2023 Australian Open, where he won his first Grand Slam doubles title as a wildcard alongside compatriot Rinky Hijikata.

1 ranking and comparisons to Rafael Nadal,[5][6][7][8] Kubler has spent the majority of his professional career on the lower circuits due to a hereditary knee condition that results in weakened meniscus around the joints.

[10] Kubler also spent four years of his professional career playing exclusively on clay courts to avoid further structural damage to his knees.

In April, Kubler won the first main draw professional match of his career at the Australia F3 Futures event in Ipswich, where he went on to make the final, losing to Brydan Klein.

[16] Further injuries during the year limited his play before he won the first professional title of his career at the USA F28 Futures event in Birmingham, defeating Yoshihito Nishioka in the final.

In 2013, Kubler played in Futures tournaments throughout the United States, Spain, Great Britain, Australia, Italy and Egypt, but only on clay due to ongoing knee concerns.

After a year out of the game and without a world ranking, Kubler returned to professional tennis in March at the Australia F2 and F3 Futures events in Canberra.

Although Kubler managed to make a semi-final appearance at Spain F12, the highlight of his European trip was a doubles title with compatriot Alex Bolt at the Italy F14 tournament.

In October, Kubler won through qualifying at the Traralgon ATP Challenger and made a remarkable run to the final after defeating two former top 100 players in Taro Daniel and Matthew Ebden.

Following an impressive run of form and a huge improvement in ranking over the past six months, Kubler was awarded the final wildcard into the 2018 Australian Open, his first Grand Slam appearance in eight years.

Following the French Open, Kubler proceeded to lose in the first round at his next three Challenger tournaments before making a semi-final run at the Ilkey Trophy, where he eventually lost to Oscar Otte.

Kubler then entered the Wimbledon qualifying tournament and showed good form through his first two matches, defeating Arthur De Greef and Adam Pavlásek.

As the fourth seed, Kubler dropped just one-set the whole tournament to claim his second Challenger title of the year, defeating Lucas Miedler in the final.

Despite losing in the final round of qualifying, Kubler was granted entry into the main draw as a lucky loser after Nick Kyrgios withdrew with a hip injury.

Taking Kyrgios' seeding, Kubler progressed through to the second round via a bye before losing in a third set tie-breaker to fellow Australian James Duckworth.

[29] At the US Open, Kubler upset 19th seed Roberto Bautista Agut in straight sets in the first round to claim the first main draw grand slam win of his career.

[30] In the second round, Kubler was forced to retire in the fourth-set against American Taylor Fritz after rolling his ankle, which inadvertently caused further problems with his knees.

[34] With limited tournament preparation, Kubler was defeated in the first round of the Australian Open by unseeded Italian Thomas Fabbiano in four sets.

Following a three-month break from the tour due to knee ailments,[35] Kubler returned in mid-April at the Kunming Challenger where he was defeated by James Duckworth in the third round.

Kubler lost the Winnetka final to top-seeded American Bradley Klahn but bounced back to win the Gatineau tournament without dropping a set.

Following a first-round exit in Australian Open qualifying, Kubler made a run to the semi-final of the Burnie Challenger before losing to Yannick Hanfmann in straight sets.

[38] In late March and early April, Kubler won back-to-back Futures events in Canberra and in May made the semi-final of the Zagreb Challenger.

The ATP, WTA and ITF all stripped the tournament of ranking points, following the All England Lawn Tennis Club's decision to ban Russian and Belarusian players from competing.

[48] He then defeated compatriot James Duckworth in straight sets to reach his maiden ATP semifinal, where he lost to 3rd seed Alexander Bublik.

Later that month, at the 2022 Atlanta Open, Kubler reached the final in doubles with compatriot John Peers, but lost to second seeded Australian duo Thanasi Kokkinakis and Nick Kyrgios.

In September, at the San Diego Open, Kubler reached his second ATP doubles final of the season, this time with fellow Australian Luke Saville.

At the Adelaide International 2 event, Kubler received a wildcard into the main draw and continued his good form, defeating Tomás Martín Etcheverry in the first round.

In March he made his Masters 1000 debut at the 2023 BNP Paribas Open where he reached the third round defeating 21st seed Grigor Dimitrov after his retirement.

In April, at the 2023 U.S. Men's Clay Court Championships, he reached the quarterfinals defeating wildcard Fernando Verdasco and Daniel Elahi Galán.

At the 2024 Australian Open, where he entered as a wildcard, he lost this time to Daniel Elahi Galan, who needed almost five hours to the minute to win his first round match.