The Oscar-winning actress will star alongside Tom Cruise, who is reprising his role of fighter pilot Pete "Maverick" Mitchell for the sequel.
Connelly's role is understood to be that of a single mother running a bar near the airbase.
Directed by Oblivion director Joe Kosinski, actor Val Kilmer will also reprise his role of Tom "Iceman" Kazansky.
Another new addition to the film, Miles Teller, was announced earlier this month.
The 31-year-old actor will play the son of Maverick's former wingman, Goose, who was killed-off in the 1986 original.
British actor Nicholas Hoult was also understood to be in the running for the part, but was beaten at the final hurdle by Whiplash actor Teller.
What's it like to work with one of the world's best-known actors on a franchise that will soon gross over $300bn?
Teller tweeted his casting success quoting a famous line from the original film: "I feel the need..."
Top Gun: Maverick is scheduled for release in July 2019.