The 41-year-old departs in the wake of the arrival of new manager Tim Sherwood, who was named as Paul Lambert???s permanent replacement on Saturday.
A former full-back who played for Arsenal, Brentford and Scotland U21, among other teams, Marshall had been at Villa since June 2013, having previously worked with Lambert at Norwich.
And, when the Premier League strugglers reacted to defeat at Hull last week by sacking Lambert, it was Marshall and goalkeeping coach Andy Marshall who took charge on an interim basis for the 2-1 FA Cup win over Leicester.
Villa chief executive Tom Fox said: “I’d like to thank Scott for his efforts during his time at the football club and especially under difficult circumstances at the weekend, when he took the team for Sunday’s FA Cup victory over Leicester City.
“We wish him all the best in the future.”
It has been speculated that Swindon No 2 Luke Williams might be set to join Sherwood’s reconstituted backroom team at Villa.
But Sherwood told the Birmingham Mail: “He’s at Swindon and is in a five-year contract. You’ll never get him out, it’s a non-starter.”