The former Welsh u-21 star was out of contract at the Meadow in the summer, and the deal is a good one for Town. Moss had been impressive of late, but boss Gary Peters was not concerned about any repercussions from the transfer.
Peters told ShrewsWeb: "He would have been out of contract and he was aware of interest from other clubs in higher divisions so it was unlikely that he would sign a contract for us.
"To get £120,000 guaranteed from Crewe with a couple of months of his contract remaining is a good deal, and one we had to take it for Shrewsbury sake."
It is thought the fee will rise from an initial £120,000 to £170,000 on appearances, and there is also a 15% sell-on clause. Moss was signed on a free from Chester by former Town boss Kevin Ratcliffe.
And Peters has already vowed to invest the cash wisely to ensure a bright future for Town. He said: "We've got 40-points and instead of us getting weaker because Darren's gone we need to get stronger.
"Perhaps I need to bring in a replacement for Daren but I also want to make the squad stronger, by bringing in a couple of loans or a couple of players who can make us stronger next season, and I need to make sure I do that in the next couple of weeks."
Crewe boss Gradi said that Moss' tally of over 200 league games was key. He said: "The experience is important to us, we've got some inexperienced players in the team and we needed someone who is young but won't be fazed by the step up."