After a loan spell at Northampton Town, Walker signed a deal at White Hart Lane and has since made three appearances.
"QPR are a good, ball-playing team so I am pleased to join the club and hopefully I can improve while I am here," he told the club's website.
"I didn't really cross paths with Neil Warnock at Sheffield United because I signed scholarship terms when they got promoted and he left the following season.
"I didn't have many dealings with him but he's a good guy, a funny guy," he added.
Walker is set to make his debut against Ipswich Town on Tuesday.