The network said it has renewed all three series in the franchise from creator and executive producer Dick Wolf, including "Law & Order: Special Victims Unit" and "Law & Order: Criminal Intent."
"Law & Order," which stars Sam Waterston, Jesse L. Martin, Dennis Farina and S. Epatha Merkerson, must air for a total of four more seasons to catch up with "Gunsmoke."
The CBS western with James Arness aired from 1955-75.
The original in the "Law & Order" family has slipped in favor among viewers. Last year, it averaged nearly 13 million weekly viewers; for the season so far, with weaker lead-ins and more competition, it's drawing 11.1 million viewers.
Sibling "Special Victims Unit" draws a bigger crowd, with an average of 13.9 million viewers. The series starring Mariska Hargitay and Christopher Meloni, now in its seventh year, also ranks as NBC's No. 2 drama (behind "ER") among the advertiser-favored young adult audience.
"Criminal Intent," which stars Vincent D'Onofrio, Kathryn Erbe, Chris Noth and Annabella Sciorra, is drawing an average 10.9 million viewers in its fifth season.
Overall, NBC is struggling in the ratings and may again repeat its fourth-place showing for the season in both viewers and the young-adult demographic.