The 31-year-old prop had been with Rovers for eight years before his departure in November, and his return means that he qualifies for a testimonial next year to celebrate 10 years of service.
"I'm really proud to have reached 10 years with the club and it's a great honour for both myself and my family," he said in a statement. "The club have shown a lot of faith in me over the past 10 years and hopefully I've repaid that faith.
Hull KR chief executive Mike Smith added: "Jason is an honest professional both on and off the pitch and has given outstanding service to Hull KR during the past decade.
"He's achieved something which is quite rare within the sport nowadays and should be extremely proud of the contribution he has made to the club."
Netherton has made 174 appearances for the club since his arrival from London Broncos in 2005.