Elisabeth Sladen was born in Liverpool, England. She attended drama school for two years before joining the local repertory theatre in her home town of Liverpool. She met actor Brian Miller during her first production there and they were later married after meeting again in Manchester, three years later. Early television work included appearances on Coronation Street (1960), Doomwatch (1970), Some Mothers Do 'Ave 'Em (1973), Public Eye (1965) and Z Cars (1962). Between 1974 and 1976, she had a regular role on Doctor Who (1963) as Sarah Jane Smith, a part she has since reprised in K-9 and Company: A Girl's Best Friend (1981); The Five Doctors (1983); the Doctor Who radio serials The Paradise of Death (1993) & Doctor Who and the Ghosts of N-Space" (1996); the Children In Need skit Doctor Who: Dimensions in Time (1993); the spin-off video drama Downtime (1995) and, most recently, in the new Doctor Who (2005) series.

Other work on television has included "Stepping Stones" (1977), Send in the Girls (1978), Take My Wife... (1979), Gulliver in Lilliput (1982), Alice in Wonderland (1986) and Dempsey and Makepeace (1985). In 1980, Sladen appeared in the cinema film Silver Dream Racer (1980). Since the birth of her daughter Sadie in 1985, she has spent most of her time being a mother and housewife, but has made occasional television appearances, including in The Bill (1984) and Peak Practice (1993).

Fan reaction of her reappearance as Sarah Jane Smith on Doctor Who (2005) resulted in the production of a second Doctor Who spin-off just for her, The Sarah Jane Adventures (2007).