Her mother Ida Margaret, née Unwin,[2] was a suffragette and had studied at The Slade School of Fine Art, until "her artistic talents were lost to the drudgery of housekeeping",[6] and who impressed upon her daughter the necessity of being financially independent of men.

The family spent summers by the sea, and in 1913 they also built a small cottage at Palm Beach, on Sunrise Hill facing the lighthouse.

[2] As a teenager at her family's holiday retreat at Palm Beach, Byles would look through her telescope across Broken Bay to the bushland beyond on the Central Coast.

[8] By 1929, there was an increasing focus on organised recreation for the city and suburban population and Marie joined the two-year-old Sydney Bush Walkers Club.

In 1930, a new name for Boat Harbour was proposed by the club; bushwalker Dorothy Lawry suggested "Maitland Bay" after the steamer that was wrecked at the northern end of the beach in 1889.

[14] Over the next five years, with the support of the Federation of Sydney Bushwalkers Clubs, Byles successfully campaigned in the press for the area to be placed under public ownership.

[8] Byles was elected a trustee of the board that managed the park, and for many years organised volunteers to clear and maintain its walking tracks.

At times her party of six in China, which included Dora de Beer, Mick Bowie and Marjorie Edgar-Jones, traveled with a military escort to protect them from bandits.

During her travels through Burma, China and Vietnam in 1938, Byles often chose to stay in temples, which brought her into direct contact with non-European cultures and religions.

A collapsed foot arch meant that she was no longer able to walk long distances or climb, and she studied spirituality and meditation to find ways of dealing with her pain.

[8] By 1938 Byles left her family home in Beecroft and built her own house on bushland that she had bought in 1935 at the edge of nearby Cheltenham, adjacent to crown land.

The four-room simple cottage is built of fibro and sandstone, and the large north-facing verandah is primarily where Byles slept and lived in preference to the interior rooms.

In 1970 Byles bequeathed her property to The National Trust of Australia (NSW), which she had helped in 1946 when she was the consulting solicitor who drafted the organisation's constitution.

[2] In 1985 a dramatised documentary, A Singular Woman, was made by Gillian Coote using text from an unpublished autobiography written by Byles, along with reenactments and commentary by friends.