Midfielder Birchill, who came through the youth ranks at Vale Park before making 78 appearances for the club between 2001 and 2006, has been training with Micky Adams' men after leaving MLS side Columbus Crew in December.
"Chris is in good shape and he has a real passion to help Port Vale return to better times," said Vale boss Adams, who signed Birchill in 2006 when he was in charge at Coventry.
"He has also trained with us previously, which has already helped him fit into the squad.
"I know that Vale supporters will be looking forward to seeing him back in Burslem and we hope he can demonstrate some of the good form which made him such a fans' favourite previously."
Birchill, 28, added on the club's official website: "This is an exciting time for Port Vale and I'm pleased that Micky has given me the chance to sign for the club.
"Vale will always hold a special place in my heart and I've kept a close eye on the club's fortunes since I left, even when I was playing in America.
"Hopefully, I can now play a part in changing those fortunes for the better moving forward."