He was an alcoholic from his teenage years until the early 1930s, when he converted to Christianity and began to spread his message by inscribing the word "Eternity" in copperplate writing with yellow chalk on footpaths and doorsteps in and around Sydney, from Martin Place to Parramatta, from 1932 to his death in 1967.

In March 1916, at age 32, while working as a labourer he enlisted for World War I with the Australian Imperial Force 19th Battalion 5th Brigade AIF, entering with the 16th Reinforcements, service number 5934.

Two years later, on 14 November 1932, Stace was further inspired by the preaching of evangelist John G. Ridley MC,[8] on "The Echoes of Eternity" from Isaiah 57:15: For thus saith the high and lofty One that inhabiteth Eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones.

Several mornings a week for the next 35 years, Stace woke at 4am to go around the streets of Sydney and chalk the word "Eternity" on footpaths, doorsteps, railway station entrances, and anywhere else he could think of.

The Sydney City Council brought him to the attention of the police as they had rules about the defacing of pavements, so much so that he narrowly avoided arrest about twenty-four times.

After a period of homelessness, Stace found work as a caretaker and cleaner at the city offices of the Australian Red Cross and his local church, Burton Street Baptist Tabernacle.

He also volunteered for decades as a social worker, assisting the unemployed, addicted, and mentally ill, both through his work for Anglican minister Robert Brodribb Hammond, and later of his own volition.

[9] In 1942, at the age of 57, Stace married his partner, Ellen Esther "Pearl" Dawson, after she proposed to him, and the couple moved to 12 Bulwara Road, Pyrmont.

[10] The mystery of "Mr Eternity" was solved after 27 years when Reverend Lisle M. Thompson, who preached at the church where Stace worked as a caretaker, saw him take a piece of chalk from his pocket and write the word on the footpath.

He bequeathed his body to the University of Sydney; subsequently, his remains were buried with those of his wife at Botany Cemetery in the Eastern Suburbs Memorial Park (General 15, Row 20, no.

[21] The Eternity Man is an opera based on Stace's life, written by the Australian composer Jonathan Mills to a libretto by Dorothy Porter.