Following her rise to fame, she revealed that she had been an unmarried mother (son James, born 1967) during the 1960s when it was socially unacceptable. James Lumley's natural father is the photographer Michael Claydon and is of Anglo Indian ethnicity. The first of her two subsequent marriages was to comedy writer Jeremy Lloyd (Are You Being Served? see early career). In 1986 she married conductor Stephen Barlow; they live in London.

Lumley was awarded an OBE in 1995. She is also a Fellow of the Royal Geographical Society (FRGS). In 2006 she was awarded an honorary degree from the University of St. Andrews.

She is a noted animal rights campaigner and vegetarian. She is also a car enthusiast, whose favourite TV programme is Top Gear. Her favourite car is a Triumph Stag convertible. She has been involved with a number of charities, including The Druk White Lotus School (in Kashmir), The Born Free Foundation, Mind (the UK mental health charity), Sight Savers, The Friends of Kadzinuni and many others. She has an interest in and concern about environmental matters, and sponsors the Joanna Lumley Fellowship in Environmental Science at the University of Oxford. At the 2007 Chelsea Flower Show, Lumley had a fuchsia named after her.