He's broken the Australian record for most runs in a five-Test Aussie summer, passing Neil Harvey's 1953 record of 834 runs, as he was dismissed on 837 runs.
England's Wally Hammond and Sir Donald Bradman are the only other batsman to reach 800 runs in a five-test Aussie summer. Hammond currently holds the record on 905 runs, which he hit back in 1928-29.
But after his first double century, he was welcomed to the club by another, unlikely, member.
Batting as a night-watchman and in his final ever test for Australia, Gillespie - primarily known for opening the bowling - scored 201 not out against Bangladesh in Chittagong in 2006.
Gillespie's acknowledgment of Labuschagne's feat didn't stop with a single tweet however, he also wrote a full letter on cricket.com.au.
He began: "You now rub shoulders with Australia's greatest batters, from Bradman to Harvey, Ponting to Perry, Brown to Border, Simpson to Smith and, of course, with me, Jason Gillespie.
"Marnus, you are entrant No.42 in our group, which dates back to 1884 when the legendary former captain Billy Murdoch hammered the Poms to the tune of 211 at The Oval.
"Since then, a further 37 men and four women have joined AWATMDC, the group I founded when I batted with patience, poise and deceptive power to post 201no against Bangladesh in Chittagong in 2006."
It's a masterful letter with Gillespie also mentioning he bowed out of cricket because of the scrutiny after his double hundred.
"Suddenly people will want to know where you live, who you're with, whether you dye your hair or if your diet is plant-based or not," the letter read.
"It is no small burden and one I recognised straight away, which is why I gracefully bowed out of Test cricket after scoring my unbelievable double century and never again wore the Baggy Green.
"But you are a young man with a bright future in front of you, so I implore you to carry on, keep piling on the runs and do your teammates, family, the country and, most importantly, this club proud."
