The striker will be hoping to find his feet at London Road.
The attacker joined the club on a permanent deal after many years at Spurs, during which he looked to be one of their top prospects.
In fact, back in 2012, he was being linked with Barcelona. The then teenage Coulthirst had recently bagged a hat-trick against Barcelona in the NextGen Series and the Catalan giants were tracking the player, according to the Daily Star.
Of course he never made the move to Barca and never made the grade at Tottenham either.
In the summer he was loaned out to Wigan Athletic of League One after previous spells with the likes of Leyton Orient, Torquay United, Southend United and York City.
But Coulthirst was recalled by Spurs after a poor time at the DW Stadium for the former England under-19 international.
He suffered with injuries and the 21-year-old managed just 53 minutes of football with Wigan since August.
Now Spurs have decided that the time has come for the striker to leave and in fairness it is probably the right decision.
For whatever reason he has never quite kicked on and at Peterborough he will have the chance to play regularly and hopefully rediscover his spark.
If he does than League One should watch out.