The talented teenager made 11 first team appearances last season in League Two, and adds versatility and flexibility to Neal Bishop's squad.
Capable of playing anywhere down the left-hand side, the youngster was part of the Scunthorpe side that defeated the Holy Blues in last season's Lincolnshire Senior Cup Final at Glanford Park.
On his arrival, Lewis said: "I’m really excited to play some games and get a good amount of minutes under my belt.
"Obviously, I haven’t played much recently, so I feel it’s a really good opportunity for me to come and try and impress at a decent level.
"It will be a good test for me. I feel like I can add some extra quality to the team and hopefully bring in a few more goals and assists.
"Overall I’m just ready to get going and try to hit the ground running when I get my first minutes."
Holy Blues player-manager Neal Bishop added: "Left-back is an area we had identified for strengthening. Harry comes with good pedigree and was featuring in League Two with Scunthorpe last season.
"He will provide competition for a starting place in that position, and with a very busy month ahead, I’m delighted we have managed to get him in."
Lewis goes straight into contention ahead of Saturday’s clash with Barlow in the FA Trophy.
Photo credit: Scunthorpe United
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