Litchfield has started seven of the eight games he has played so far this term, scoring a try in the win over Leicester in the first round of the Premiership Rugby Cup at the start of November.
“I’m really happy to be remaining a Saint,” said Litchfield.
“The group we have at the club – players and staff – is really special. For me, there isn’t anywhere else I’d rather be playing my rugby.”
Director of Rugby Phil Dowson said Litchfield’s “constant improvement” is what has most impressed him in recent months.
“His differential is his physicality, his ability to get us over the gain-line in tough situations, and he does that with a really strong attitude,” Dowson said.
“We’re really pleased with how he keeps improving and showing us what he’s capable of.”
Litchfield is the second Saints player to sign a multi-year deal this week after teenage back-rower Henry Pollock.
