Austin, 18, will now remain in north London until the summer of 2019, as he continues to keep goal for Spurs' reserve side despite his tender age.
Born in Hemel Hempstead, Austin has selected to play for the United States but is yet to make his national team bow at any level, neither has he been given the chance in Spurs' first team during his short career.
Spurs announced the agreement on Twitter on Monday afternoon, which leaves Holland international Michel Vorm in a precarious position concerning his future in north London.
Vorm, 34, sees his current deal at Wembley Stadium expire in just a matter of months, and is free to talk to clubs from January 1 on a pre-contract agreement if Spurs do not offer him an extension.
The former Swansea ace could now be considered third-choice goalkeeper at Spurs, after summer signing Paulo Gazzaniga produced a number of excellent saves in Tottenham's 1-0 win over Crystal Palace last time out.
At third choice, the likelihood Vorm was going to be offered a new contract was slim. Now, with Austin putting pen to paper, it seems as though Spurs are building for the future and throwing the past on the scrapheap.
Vorm's only hope of a Tottenham contract now is to prove his worth on the training ground, but the chances are that he could be looking at a move away from Spurs in the January transfer window following Austin's contract.