Financial terms were not disclosed. GrubHub CEO Matt Maloney will become CEO of the combined company. Seamless CEO Jonathan Zabusky will serve as president.
Brian McAndrews, an independent director on the Seamless board, will serve as chairman. Both New York-based Seamless and Chicago-based GrubHub will have significant representation on the new company's board.
The combined company's name and marketing brands will be determined following regulatory approval.
Maloney, who co-founded GrubHub Inc. in 2004, said that by combining their complementary restaurant and diner networks the new company will be well positioned for continued growth in what's become a huge market.
Last year, orders through the two privately held companies totaled about $875 million in gross food sales, resulting in combined revenue of more than $100 million.
Seamless North America LLC was spun off from Aramark Corp. last fall. Before that, Spectrum Equity Investors bought a minority stake in the company for $50 million. Seamless covers about 12,000 restaurants in 40 cities, mostly on the East and West Coasts, along with Houston and Austin, Texas, and overseas in London.
GrubHub's ordering services cover 20,000 restaurants in about 500 cities. Since its inception, the company has received about $84 million in private equity funding.