The 18-year-old midfielder initially joined the Seasiders in January on an initial one-month loan from the League Two side.
He has since made eight appearances, scoring twice against Ashton United and South Shields.
On Horbury's extension, Marske United manager Curtis Woodhouse said: "I am delighted to get the extension for George, from Harrogate.
"I think he has done really really well for us in difficult times. Chipping in with two goals, putting in good displays in the middle of the park at such a tender age of 18 as well.
"I had a good chat with George the other day after the game and said in his career this will be a really good moment for him," he added.
"Not many have the chance, to get thrown into pressure games, relegation fights when you are just 18 years of age so all the experience you can draw upon from this will be valuable.
"He wants to stay with us. He wants to ‘finish the job’ were his exact words and he wants to continue the fight to keep us in the league. This shows he has got a really good mentality.
"I am really grateful to Simon Weaver at Harrogate for trusting us to help develop George and I am sure he is going to go on and have a really bright career."
Marske United are next in action at home to Warrington Town on Saturday afternoon.
Photo credit: Harrogate Town
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