Originally from San Juan, Big has been involved in music, dancing and performing since a very young age, She says “I began ballet lessons at age four and piano lessons at age six. As far back as I can remember my mom always had me involved in something.” By the age of 15 she was appearing in commercials and music videos. She then landed a job as co-host, dancer and choreographer on “Que Vacilon”; Puerto Rico’s number 1 weekly television comedy – variety show, where she starred for three years.
 
In 1993 Roselyn won the title of Miss Puerto Rico Petite, and went on to win Miss America Petite in 1994, representing Puerto Rico. Eventually she decided if her career was to take off she would have to move to New York, she left before completing her business and marketing degree at the University of Puerto Rico, this was a hard decision for her, especially as it meant leaving her family: “The only bad thing was leaving my family behind. They have always been very supportive and they knew I had to make this move. As hard as it was for them to let me go it was even harder for me to leave them. I am the youngest of four, with three brothers. It’s funny because people usually think that coming from a family where there are three older brothers and a dad, that they would be very protective. They are protective, but I would have to say by far my mom is the most protective.”

Roselyn landed her first English-speaking part -- the role of Pilar Domingo, the first-ever Latina character in the 40-year history of CBS soap opera "As the World Turns." While in New York, she also wrote and performed her one-woman show, "Out Here On My Own."
In 1997 Roselyn landed the part of Lili Arguelo, a Puerto Rican dancer, on TV series FAME L.A., after unsuccessfully auditioning for a part on a new Damon Wayans sitcom. Sanchez, delighted about getting the part said: ‘Fame gives me the opportunity to do all that I love, acting, singing and dancing,’

Sadly, Fame L.A. only lasted one season, however Roselyn was not deterred and moved on to other projects, including a role in the 1999 movie HELD UP starring comedian Jamie Foxx. As well as guest starring in a number of TV shows, Roselyn gained a starring role in TV series RYAN CAULFIELD: YEAR ONE as police officer Kim Veras, for FOX television.

However Roselyn's next big break would be in the 2001 movie, the hugely successful RUSH HOUR 2, sequel to the hit comedy movie starring Jackie Chan and Chris Tucker as a mismatched crimefighting duo.  Roselyn played the part of Isabella Molina, an undercover secret service agent, and also a love interest for Chan's character.
Following the success of RUSH HOUR 2 Roselyn has been busy shooting a number of different films and other projects, the first of which was the comedy movie BOAT TRIP, recently seen in cinema across Europe. The film also starred Cuba Godding Jr, and Roger Moore, but to name a few. Roselyn played the female lead, 'Gabriela.

The near future sees the release of the Fox 2000 comedy movie PAPI CHULO (or CHASING PAPI) which sees Roselyn as the lead character in a trio of women who set out for revenge when they discover they have all been dating the same man.

Roselyn has also been busy filming the action/adventure movie BASIC starring the likes of John Travolta and Sam Jackson; as well as becoming the spokesperson for the Pepsi softdrink SIERRA MIST, she has also appeared on ABC television's special, DISCO BALL, which saw her singing live for the first time on TV, and has just presented on both the LATIN GRAMMY awards and the HISPANIC HERITAGE AWARDS.