The athletic 25-year-old openside, who left Australia to play for the Suntory club in Japan after finding his test chances blocked by Michael Hooper and David Pocock, will return to the squad for next weekend’s World Series leg in Cape Town.
“I’m really looking forward to representing my country again,” said McMahon, who played the last of his 26 tests against Scotland in 2017.
“The Australian sevens team have been building well following their qualification for the Olympics next year and I’m looking forward to putting my hand up for the campaign.
“I would like to thank Suntory for being supportive of my decision, to share my duties across the two teams.”
Australia were knocked out of the quarter-finals by Samoa in the opening leg of the 2020 Sevens World Series in Dubai at the weekend.
“Sean is a fierce competitor, mobile forward and is the kind of athlete that is perfect for the intensity of Sevens and he wants to put himself in contention (for) the 2020 Tokyo Olympic Games,” said Australia coach Tim Walsh.