The pacy 19-year-old, who has represented England at under-19 level, has made one first-team appearance for Spurs in the FA Cup win over Charlton in January, when he got on the scoresheet.
Townsend recently returned to White Hart Lane following a month on loan at Watford, where he was restricted to only three appearances.
The teenager was supposed to spend the season on loan at Ipswich after joining them in August but the deal was cut short when he fell out of favour at Portman Road.
The Londoner has spent the majority of the last three seasons out on loan, having spent time at MK Dons, Leyton Orient and Yeovil.
Townsend will go straight into the Lions' squad to take on Championship table-toppers QPR at the Den on Tuesday.
Source: PA
Source: PA