Roslin is the daughter of the former BBC radio announcer Clive Roslin, who was born and raised in London. Her family is Jewish, originating from Zimbabwe (then Rhodesia). She attended the North London Collegiate, London Independent school, and then the Guildford School of Acting and followed a career in television presenting.

Roslin first presented Hippo on the Superchannel and then Motormouth on ITV from 1989 until 1992. At the end of that show she was approached by Planet 24 to present their new early-morning programme The Big Breakfast alongside Chris Evans. Evans left the show in 1994 and Roslin continued with his replacement, former Neighbours star Mark Little, until 1996.

Roslin presented Children in Need Read more...

Roslin married musician Colin Peel in 1995; they divorced in 2004. They have a daughter, Libbi-Jack, born 2001. In December 2006 Roslin had another daughter, Amelie, from her relationship with publishing boyfriend David Osman.

Gaby is a patron of children's cancer charity CLIC Sargent.