She joins her former co-star David James Elliott, who will reprise Capt. Harmon "Harm" Rabb, Jr.
Elliott will first appear in the May 12 episode of "NCIS: Los Angeles," with Bell to return in the Season 10 finale, which airs May 19.
"Catherine's Mac was a strong, smart woman who held her own, and then some, in a male-dominated world," "NCIS: Los Angeles" executive producer R. Scott Gemmill said in a statement.
"Her character paved the way for other strong female leads."
"Not only is great to be working together as friends, but to be able to write for Catherine and have her same character interact with our 'NCIS: Los Angeles' characters now, that's wonderfully surreal," he added.
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"It feels like everything has come full circle."
Bell had teased her return in an Instagram post Monday.
"Tired but so happy. What an amazing day on set. Can't WAIT to share what I'm doing .... and the people I'm working with," she wrote.
Deadline said Bell and Elliott are also expected to appear in the first two episodes of "NCIS: Los Angeles" Season 11, although the show has yet to be officially renewed.
The pair's return has let to speculation of a "JAG" reboot or revival.
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