Two of the networks are majority black-owned while two are majority American-Hispanic-owned, with all of them programming in English, the Philadelphia-based Comcast said.
It was unclear how much of an on-camera role, if any, Combs and Johnson might play on their respective network.
The new channels, which in all will total 10 rolling out in the next eight years, are part of an agreement reached by Comcast with the FCC and Department of Justice when it was allowed to become majority owner of NBCUniversal.
The networks announced Tuesday include:
— Revolt, conceived by Combs and MTV veteran Andy Schuon, will have programming that includes music videos, live performances, music news and interviews.
"Revolt is the first channel created entirely from the ground up in this new era of social media," said Combs, who described the channel as "immediate, like today's social networks."
In a video posted on YouTube, Combs said Revolt will put artists in charge.
"It's your channel to do what you want to do, how you want to do it," he said, addressing them, with the result "uncut, raw, uncensored."
Revolt is scheduled to launch in 2013.
— Aspire, to be led by Johnson in partnership with family-oriented channel GMC TV, will dedicate itself to enlightening and positive programming aimed at black families. It will air movies, documentaries, music and comedy, as well as faith and inspirational programs.
"Aspire will be a network that encourages and challenges African-Americans to reach for their dreams," said Johnson, adding that it "will celebrate our heritage, our groundbreaking achievements and the fearless talent that has shaped American culture."
It will launch this summer.
— El Rey, proposed by Hollywood director Robert Rodriguez and FactoryMade Ventures executives John Fogelman and Cristina Patwa, is designed to be an action-packed, general entertainment network for Latino and general audiences. The programming mix will include reality, scripted and animated series, and will feature Hispanic producers, celebrities and public figures.
"We are passionate about creating a wildly entertaining destination that we can be proud of by appealing to both Latino and mass market audiences," said Rodriguez, a successful filmmaker known for the "Spy Kids" films.
El Rey is scheduled to debut by January 2014.
— BabyFirst Americas, from Spanish-language TV veteran Constantino "Said" Schwarz, is designed for infants and very young children, as well as their parents. It will emphasize the importance of early development of verbal, math and motor skills, the network said.
"BabyFirst Americas aims to bring the essential academic building blocks for kindergarten readiness into the home," Schwarz said.
The first of the networks to arrive, it is planned to be on the air this April.
These four networks, and the six others yet to be announced, are being chosen from more than 100 proposals, Comcast said. Each will be added as part of Comcast's digital basic tier of service.
The company, which is the nation's largest cable TV provider, did not mention in its announcement other cable systems planning to carry the new networks.