According to a source, Hall agreed to a one-year deal that is worth $492,000 for the remainder of the season, the prorated portion of his $1 million base salary that he would have received from the Oakland Raiders.
"He's excited to be coming home, he's a Virginia Tech guy," agent Joe Segal told The Associated Press.
The Raiders released Hall on Wednesday, eight games into a seven-year, $72 million contract.
He walked away with $8 million this year and a chance to sign with a new team, which he did Saturday after passing a physical.
The Redskins waived cornerback Leigh Torrence to make room for the two-time Pro Bowler.
Torrence played in all 16 games last season as well as all nine games this year after joining the Redskins as a free agent in December 2006.
A source close to the Redskins said Hall spoke with Redskins coach Jim Zorn and some of Zorn's assistants before accepting a contract, and that team owner Daniel Snyder met with defensive captains London Fletcher and Cornelius Griffin to gauge their opinion of the move.
The Redskins are on a bye, so Hall won't make his first appearance in a Redskins uniform until Nov. 16, when Washington plays the Dallas Cowboys.
But Hall did struggle in coverage early in the season; he had shown signs of improvement in recent weeks, but was let go anyway following a 24-0 loss to the Atlanta Falcons that dropped Oakland to 2-6 on the season.
In his eight games in Oakland, Hall was beaten 40 times for 552 yards on 66 passes thrown his way, according to data compiled by STATS. He gave up more yards than any defender this season and was tied for third worst in catches allowed.
Senior writer John Clayton covers the NFL for ESPN.com. Information from ESPN.com NFC East blogger Matt Mosley and The Associated Press was used in this report.