McGrath joined MTV in 1981 writing on-air prompts and helped to develop the animated interstitial IDs that defined the network. She moved up the ladder to editorial director, creative director, and, in 1991, executive director sharing control of the entire network operations with Sara Levinson. Besides developing programming, McGrath kept MTV on track as a style setter for the youth of the world. It has been said that all VJs (music video hosts) must be under 30 years of age and that McGrath even had approval to change wardrobes. Additionally, she has been said to approve the videos to be played, keeping the network geared towards rock'n'roll and--much to the criticism of some--away from R&B and, often, relegating rap and hip-hop to only specific programs. McGrath also spearheaded the "Choose or Lose" election coverage on MTV in 1992.

As its initial music-only format waned in popularity, the network has diversified with dance and dating programs (i.e., "The Grind", "Singled Out"), documentaries and reruns of network shows (e.g., "My So-Called Life") Shows such as "The Real World", in which several college-age youths are roomed together for cinema verite, have won MTV much press coverage as has the animated "Beavis and Butt-head", although much for the latter has been negative. McGrath moved to the big screen as executive producer of MTV's maiden voyage into feature film production, "Joe's Apartment" (1996).