Ramírez was born in Santo Domingo, Dominican Republic. From an early age, Dania knew that she wanted to be in front of a camera. As a young child, she would reenact Spanish soap operas for her family. She was discovered by a modeling scout while working in a New York City convenience store at the age of 15, and was cast in a small part in a soda commercial. Years later, she decided to pursue acting seriously and studied at the Actor's Workshop in New York City under Flo Greeberg. After completing a degree at Montclair State University in New Jersey, she moved to Los Angeles.

She made her acting debut as an extra in the HBO film Subway Stories (1997), where she met filmmaker Spike Lee who later cast her in his film, She Hate Me (2004). Dania appeared as Potential Slayer Caridad in the final episodes of the television series Buffy the Vampire Slayer, as Callisto in the comic book film X-Men: The Last Stand (2006), and as Blanca Selgado (A.J. Soprano's new love interest) in the first part of the sixth season finale of The Sopranos. On The Sopranos, she played a single mother with a three-year-old son, Hector. She also appeared in LL Cool J's video, "Hush", which was directed by her fiancè, Jessy Terrero.

Currently, Ramirez portrays the character of Maya on the TV series Heroes.

In 2007, she appeared in the music video for Santana's "Into the Night" (featuring Chad Kroeger from his album Ultimate Santana.