The order would also approve Sprint's acquisition of wireless network operator Clearwire, which owns the rights to valuable swathes of wireless frequencies.
The FCC approval is the final obstacle to the pair of telecom deals.
SoftBank's acquisition of Sprint could pump more money into the company and help it take on industry leaders AT&T and Verizon.
Dish Network had pushed its own competing proposals for both Sprint and Clearwire, but recently abandoned its bid.
Dish had warned that allowing SoftBank, a Japanese company, to own such large U.S. telecommunications networks would pose a threat to national security. Sens. Charles Schumer (D-N.Y.) and John McCain (R-Ariz.) also expressed concern about the SoftBank deal.
After SoftBank agreed to a series of concessions, an interagency panel cleared the deal of national security concerns in May.