Smith has switched from No. 54 to No. 9, which he sported at Notre Dame and in high school while Romo donned it in Dallas. No Cowboys player has been issued the number since the quarterback-turned-broadcaster retired in 2017.
The four-time Pro Bowler wore No. 9 for all of his 14 NFL seasons.
"It's just a blessing and honor to be able to carry on the 9 legacy," Smith told reporters following Tuesday's OTA session, per the Dallas Morning News.
Romo and Smith were briefly teammates in 2016, though neither hardly played because of injuries. The QB was limited to just one appearance after a preseason injury sidelined him for the first two months of the season. Smith sat out his entire rookie campaign to recuperate from a torn ACL and MCL suffered in his college finale.
After being selected in the second round, the Notre Dame star chose to wear 54 because the digits added up to nine. Dallas has yet to formally retire numbers, though a few have remained unassigned after being worn by Hall of Famers, including Nos. 8 (Troy Aikman), 12 (Roger Staubach) and 22 (Emmitt Smith).
The team also announced safety Donovan Wilson is switching from No. 37 to No. 6, which he also wore in college.