"With the loan window closing I felt we needed another striker to see us through the next month or so," boss Ian Sampson told the club website.
"December is a busy time and we need more options up front."
He added: "I think Ryan can come here and do a good job. He is a player with a very good engine and works hard for the team.
"He has played all of his football at a decent level and has a good amount of experience.
What can us Cobblers fans look forward to/expect from him in his time at Sixfields?
NTown_Fan
"He will be a good foil for the other players we have here and I am pleased to welcome him to the club."
Jarvis will link up with former team-mate Leon McKenzie, who he played with at Norwich City for two and a half years.
He started his career with the Canaries, where he made 48 appearances but just 11 starts across five years, scoring five goals.
Loan spells at Colchester, Orient, Kilmarnock and Notts County followed before he signed permanently for the O's in the summer of 2008.
Since then Jarvis has scored 13 goals in 95 games and signed a new one-year deal at Brisbane Road six months ago.
Source: BBC Sport
Source: BBC Sport