Tim Paine stepped down as Test captain last week over a sexting scandal.
Paine quit as Test skipper over the public revelation of an exchange of allegedly sexually graphic text messages with a female colleague in 2017.
"I am honoured to accept this role ahead of what will be a massive Ashes summer," said Cummins in a statement.
"I hope I can provide the same leadership Tim (Paine) has given the group in the past few years.
"With Steve (Smith) and I as captains, a number of very senior players in this squad, and some great young talent coming through, we are a strong and tightly knit group."
The recent turn of events also led to Steve Smith’s return to a key leadership role as he has been named the vice-captain of the Test side, having been forced to stand down as skipper for his involvement in the 2018 ball-tampering scandal.
Coming to Pat Cummins, he becomes only the second specialist fast bowler to captain Australia’s Test side after Ray Lindwall, who led for one Test against India in the 1950s.
Meanwhile, Cricket Tasmania on Friday confirmed that Tim Paine would leave all forms of the game for the “foreseeable future”, leaving Australia's Ashes preparations in disarray.
The Ashes 2021-22 is due to get underway on December 8 at Gabba.
(With Reuters inputs)