Walton expressed his excitement about returning permanently. "I'm absolutely delighted to be back.
Dundee United is a club that means a lot to me," he said.
The goalkeeper recalled the achievements from his previous tenure, including promotion and European qualification.
"Winning promotion and then helping the club achieve European football made it a really special period," Walton added.
Walton stated he was keen to make the move happen as soon as the opportunity arose.
"As soon as I became aware of the opportunity to come back, it was something I really wanted to make happen," he said.
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The transfer leaves Preston North End with Daniel Iversen and Li-Bau Stowell as their contracted goalkeepers, while contract discussions continue with Dai Cornell.
