The winger was released by Coventry at the end of last season and has said he is relishing the chance to get back to competitive football.
Speaking to the club's official website, Marshall said: "Any person that plays football out of love will know it is always good to have the opportunity to play in a professional league and Port Vale has a lot of history so I'm happy to be here.
"I've been around the block a few times since starting out at Carshalton Athletic, and I'm now looking for somewhere to settle and I hope that will be Port Vale.
"The biggest thing for me as a player, is feeling wanted and when I spoke to Micky he talked about how he wants to progress and wants his team to progress. That vision really suits me so it wasn't really a hard decision in the end to be honest.
"When I had my time off, I realised how much I loved football. I'd go to the park every day and kick a ball around on my own and I'd just feel the buzz.
"So going out in front of just one fan is something special to me and makes me happy. so playing to the fans at Vale Park is going to be amazing."