The Borders club have acted swiftly to replace Wright who stepped down on Saturday.
Marshall will work alongside another former Selkirk player in Michael Jaffray and the pair will be assisted by Kieran Cooney and Fraser Jack.
Marshall previously enjoyed success in Selkirk, boosting age group rugby by taking the local Youth Club to three Scottish under-18 finals, winning in 2003. The former Scotland flanker then took over as Selkirk head coach in 2010/11 season. He left to become head coach at Heriot’s.
Selkirk’s acting director of rugby John Rutherford said: “We were disappointed to lose Peter as he was so popular with our players and supporters, however we are delighted to secure the services of Graham Marshall and Michael Jaffray, both excellent coaches in their own right.”
Marshall will take charge for the first time on Friday night when Selkirk travel to take on Jed-Forest in the Border League.