A democratic candidate for the seat, Burlington County Freeholder Aimee Belgard, has aleady registered her candidacy with the Federal Election Commission, but the GOP has yet to find a replacement for Runyan.
A formal announcement is expected later on Wednesday.
Rep. Tim Griffin (R-AR), also a two-term congressman, announced in October that he would not seek a third term.
National Republican Congressional Committee Chairman Greg Walden released a statement Wednesday praising Runyan's work in Congress following the news of his retirement:
It has been an honor to serve with Jon Runyan. Jon is a humble and thoughtful public servant who has been a dedicated representative for his New Jersey constituents, always putting what’s best for them first. Jon came to Congress to help get our country back on track, and since day one, he has been an important part of our efforts to reform the federal government and get reckless spending under control. While Jon will be missed, I wish him and his family all the best as they start the next chapter of their lives.