The Men of Gwent are without four of their five recognised midfielders with Tyler Morgan, Jack Dixon, Pat Leach and Ross Wardle sidelined by injuries.
They had brought Ospreys centre Ben John to Rodney Parade for a month, but the 23-year-old’s spell was cut short by a hamstring problem.
Wales call-up Tom Prydie has impressed in his makeshift role at number 13 in the last couple of matches, but Director of Rugby Lyn Jones has opted to give Williams his chance in the regional limelight.
The 26-year-old came through the Scarlets Academy before going on to play professionally in France for Nevers. Williams signed for the Quins in 2013 and scored 12 tries in his first season with the club. He played at inside centre last weekend when British and Irish Cup holders Leinster A were turned over in Carmarthen.
Director of Rugby Jones commented: “I would like to thank Carmarthen for loaning him to us for a month. Rhys is a talented player who has always stood out as one of the best players in the Premiership – he deserves a chance in Regional rugby.”
The Dragons face a daunting trip to Ulster on Friday after Taulupe Faletau, Hallam Amos and Tom Prydie were called into the Wales squad for the Dove Men International Series.
The LV=Cup returns a week later with tests against Harlequins and Ospreys awaiting the Gwent region, and Morgan could make his comeback when the PRO12 resumes at the end of November.
