Her most notable television roles are as María LaGuerta on Showtime's Dexter, Detective Nina Moreno on Fox's New York Undercover, Dr. Gloria Nathan on HBO's prison drama Oz, and Elena on ABC's comedy-drama Ugly Betty.

Vélez's father, a New York City Police Department officer, eventually bought a house in Far Rockaway, Queens, and moved the family there.

The twins staged improvised plays and acting for the family and participated in nearly all their high school drama productions, such as Fiddler on the Roof.

In 1994, Vélez made her film debut as Lisette Linares in the movie I Like It Like That alongside Rita Moreno and Jon Seda.

[4] In 1995, Vélez landed her first major television role as Nina Moreno, a policewoman, in the TV series New York Undercover.