Production on the project was suspended in December after Lively sustained an injury while filming on location in Dublin, Ireland.
Lively has made a fully recovery with The Rhythm Section set to resume production in Spain, The Hollywood Reporter noted citing sources.
Details about Brown's character are being kept under wraps. Jude Law also stars in the film, which is from director Reed Morano (The Handmaid's Tale).
The Rhythm Section, based on a novel by Mark Burnell, will follow Lively as she seeks revenge after her family in killed in a planned plane crash.
Paramount is still planning on releasing the film on Feb. 22, 2019, Deadline reported.
Brown stars on NBC's This Is Us and will next be seen in actioner Hotel Artemis.