Walker, 19, features at right-back and has been on trial with the Steels during pre-season and played in the club's friendlies against Spennymoor Town and Sheffield Wednesday.
He came through the Doncaster Rovers academy and spent last season with Toolstation Northern Counties East Division One side Rossington Main, where he made 10 appearances.
Following the completion of the signing, manager Chris Hilton said: “Elliot is an excellent player with great potential to move up the leagues.
“We look forward to helping in his development.”
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