The left-sided midfielder, renowned for his speedy and tricky wingplay comes to Scarborough having worked with Darren Kelly at Hyde United.
Porritt, 24 has recently enjoyed spells with Ossett United and Tadcaster Albion on loan, and will go straight into tomorrow's squad for the home game with Bamber Bridge.
Boss Darren Kelly added: "Luke is a player I have known from Hyde and is fully aware of my training methods, intensity and what I am trying to implement here at Scarborough.
"Luke is one of the fittest players I have managed in non-league and his work rate is second-to-none".
Porritt also reunites with former tiger, Harry Coates at the seaside. Luke is available for selection tomorrow.