"It's his just reward for his performances," Warnock told the club's official website.
"We're building for the present day as well as the future and he's the type of football player we want at this club."
Warnock continued: "He's a key member of the squad and we're delighted he agreed an extension."
Ephraim added: "I'm very happy. I was in the last year of my contract, so I'm just delighted we've managed to get it sorted after a few months of negotiating."
The young Londoner initially joined the R's on loan from West Ham United in 2007 and became a permanent fixture at the club in 2008.
Source: BBC Sport
Source: BBC Sport