The 21-year-old has scored 28 points in Scarlets' past two games, including 17 in Sunday's 22-22 European Champions Cup draw against Saracens.
Scarlets boss Wayne Pivac said: "He has held his own against some of the most experienced fly-halves in world rugby."
Jones said: "Hopefully I can repay the coaches for their faith in me."
Fly-half Dan Jones has signed a contract extension that will keep him at Scarlets for what the region describe as "the next few years".