Born and raised in England, he contracted African trypanosomiasis at the age of twelve and suffered from narcolepsy for the rest of his life.

That year, Jenner encountered a group of men from the Glanton Exclusive Brethren who were engaging in open-air preaching, and he converted to Christianity.

For 28 years, from his initial conversion until his debility from Parkinson's disease, Jenner engaged in personal evangelism, probably speaking with more than 100,000 people in total.

In 1952, the Reverend Francis Dixon of Lansdowne Baptist Church in Bournemouth, England, began hearing several testimonies from people who became Christians after Jenner accosted them on George Street, Sydney.

On the way, while the ship was docked at a port in West Africa, a tsetse fly bit Jenner and infected him with Trypanosoma; he therefore contracted African trypanosomiasis, which is also called "sleeping sickness".

From this point on, he suffered from excessive daytime sleepiness and was eventually diagnosed with narcolepsy,[1] which prevented him from ever being able to drive a car.

[3] In 1937,[10] Jenner encountered a group of men from the Glanton Exclusive Brethren[11] standing in front of the National Australia Bank on Collins Street.

Jenner converted to Christianity and, when he went home, told Jessie she was a sinner bound for hell and therefore in need of salvation.

Consequently, she and Ann moved to India to live with Jenner's aunt Emily McKenzie, who ran the Kotagiri Keswick Missionary Home.

[15] For the rest of his life, Jenner attended Open Brethren churches: one on Goulburn Street in Sydney and the other in Bexley, New South Wales.

[16] At these churches, people did not understand what narcolepsy was and thought Jenner was consistently falling asleep during services because he lacked respect for God.

[15] Out of gratitude to God for giving him salvation, Jenner committed to consistently engaging in personal evangelism, and aimed to talk with ten different people every day thenceforward.

"[19] While engaging in these activities, Jenner would normally wear a white shirt, black shoes, and trousers, and sometimes a navy greatcoat.

[10] Usually evangelising on George Street, Sydney,[20] Jenner asked many people the same question: "If you died within 24 hours, where would you be in eternity?

[22] On Saturday nights during the war, Jenner would invite groups of sailors to his home for a service consisting of some hymns and a short sermon.

[3] One of the people to whom Jenner posed his question was Noel Stanton,[23] a man from Bedfordshire, England, who was serving in Sydney[24] with the Royal Navy at the time.

[26] In 1952,[27] another person Jenner accosted with his question on George Street was Ian Boyden, a man from Roseville who was serving in the Royal Australian Air Force.

[23] The following year, Dixon heard two different British sailors who did not know each other testify at Lansdowne Baptist Church, and both had told very similar stories to Culver and Stanton; both had been walking down George Street and had been asked Jenner's question.

[36] At a Methodist church in Perth, Dixon told Culver's, Stanton's, and Wilkes' stories again, and met yet another person who had become a Christian after an encounter with Jenner.

He was then diagnosed with colorectal cancer and spent a subsequent ten days at Calvary Hospital, Kogarah, New South Wales, where he died at 11:45 pm on 8 May 1977 at the age of 73.

[29] Many storytellers said Jenner was small in stature and that he had white hair; this description is contradicted by interviews with family members.

Wilson wrote that Jenner was "eccentric ... the very antithesis of the 'wise', 'mighty', and 'noble'," but that his life was therefore a good demonstration of 2 Corinthians 12:9,[16] which states that God's "power is made perfect in weakness.

"[44] Wilson wrote that he "travelled and corresponded widely to ascertain the facts of the story" and that he personally verified the accuracy of the information by retrieving first-hand accounts from all the major figures in Jenner's life.

[29] The people Wilson interviewed included Nancy Dixon; Ann and Angus Carruthers, Jenner's daughter and son-in-law; Murray Wilkes; Ian Boyden; Tas McCarthy; Peter Culver; Noel Stanton; and Mary Stares.

[47] One such account was recorded by Ray Comfort on the Living Waters website and then repeated in the 2006 book Spirit-led Evangelism: Reaching the Lost through Love and Power by Ché Ahn.

[50] These details contradict the information provided by Wilson, who writes in his biography that Jenner died more than twenty years after Dixon told him about the people who had become Christians as a result of his evangelism.

[51] Claire Goodwin encouraged people to emulate Jenner by including an account of his evangelism in her 2013 book Compelled to Tell: A Fascinating Journey from a New York Dead-End Street to a Lifetime of Ministry and Soul-Winning.