Marshall, whose current deal was due to run out this summer, has put pen to paper on a 12-month extension.
The 35-year-old had previously played for Norwich, Millwall and Coventry and provides back-up to Brad Friedel.
Marshall said: "To be able to renew my contract and get a third year, I am absolutely delighted.
"I've been fortunate enough to be sat behind Brad Friedel for the last two years and hopefully now I can push on and see if I can get to the next level.
"Everyone wants to play but being behind Brad you also have to be realistic of the level he is playing at."
Source: PA
Source: PA