Adam Stern and John Ourand of SportsBusiness Daily were the first to report the news and added that Junior's deal will begin in January.
Stern and Ourand also reported that Earnhardt signed with NBCUniversal rather than NBC Sports, and it is expected he will be used in a capacity that isn't exclusive to NASCAR.
Since NBC only carries the second half of the NASCAR season, it was speculated that the 42-year-old could be used as part of NBC's NFL and Olympics coverage.
Earnhardt is in the midst of his 19th and final NASCAR Cup Series season after announcing his upcoming retirement earlier in the campaign.
He missed the final 18 races of 2016 due to concussion-like symptoms and has struggled thus far in 2017 with only four top-10 finishes to his credit.
Earnhardt is currently 22nd in the standings, and a playoff berth is unlikely unless he manages to win a race prior to the start of the Chase.
The two-time Daytona 500 winner is a natural fit as an on-air personality, having won NASCAR's Most Popular Driver Award every year since 2003.