Beaumont took charge of England's innings and nearly carried her bat before becoming the last wicket to fall for 208 - the fifth-highest score in women's Test cricket.
She walked off to a standing ovation and fist-bumps from young fans near the pavilion at Trent Bridge after England were all out for 463, giving Australia a first-innings lead of 10 runs.
"I can't quite believe it... I scored a double hundred in the 'A' game last week (201 against Australia A) and thought there's no chance I'd repeat it," Beaumont told Sky Sports.
"To get nearly level to the Aussies today was obviously the goal and to contribute in that way was great... I was in the zone."
England had 19 overs to make inroads into Australia's batting lineup but openers Beth Mooney and Phoebe Litchfield held firm to reach 82-0 at stumps.
Resuming on 218-2, England nearly lost Nat Sciver-Brunt to the first ball of the day when Darcie Brown successfully appealed for lbw, but the home side reviewed the decision and she survived as replays showed the ball was missing leg stump.
Sciver-Brunt completed her half-century but Ashleigh Gardner's spin produced an edge and Alyssa Healy took the catch behind the stumps to send her back to the pavilion for 78.
Beaumont continued to attack before Danni Wyatt fell six short of a half-century on debut when she nicked Brown to second slip.
Australia used eight different bowlers and the 32-year-old Beaumont nearly threw her wicket away when she was on 199, going for a non-existent run before she was sent back by Sophie Ecclestone, giving her teammate a sheepish smile and a thumbs-up in return.
She regained her composure and flicked the next ball off her hip to fine leg to become the eighth woman to score a test double century, with former Pakistan player Kiran Baluch's record of 242 within reach.
Australia's Tahlia McGrath dismissed Ecclestone, Kate Cross and Lauren Filer in successive overs and Beaumont was bowled by Gardner.
"I'd say we have the upper hand just a little bit. I think in the second innings for the English girls it's going to be pretty hard to bat on," Gardner told the BBC.
"I think it's a wicket where if you miss the stumps it's a free hit and Tammy showed that. Whenever we missed the wickets she hit the ball to the boundary."
