Khoo Oon Soo was born in Penang on December 26, 1919, the first son among 10 children of Reverend Khoo Cheng Hoe and his wife Kwan Chin Poh.

Loh Siew Lan was also born in Penang on February 15, 1919 into a staunch Buddhist family. Her father died when she was very young and her grandmother, the head of the family, was illiterate but knew that a Christian school would provide good moral teaching. And so Siew Lan was sent to the then Anglo-Chinese Girls School (renamed the Methodist Girls School in 1945) in Penang, where she became a Christian.

Siew Lan attended the Chinese Methodist Church in Madras Lane, Penang and met Oon Soo at the Methodist Youth Fellowship there. Her future father-in-law Reverend Khoo was the pastor of the English-speaking congregation of the church and led the Youth Fellowship group. Oon Soo and Siew Lan served actively in the church and the Youth Fellowship and he was instrumental in forming the church orchestra. 

In late 1938, Dr John Sung conducted evangelistic meetings at the Madras Lane Chinese Methodist Church and trained disciples to preach the Good News. Oon Soo and his younger brother Oon Teik were chosen to preach on the streets of Penang. 

Oon Soo had intended to be an architect but the Japanese occupation of Malaya put a halt to those plans. After World War II, Oon Soo was appointed by the British government to become Malaya’s first ever probation and parole officer. The couple were married in 1947. In 1948, he was awarded a scholarship by the British government to study social science at the London School of Economics. In London, Oon Soo attended the Boys Brigade Training Centre at Avon Tyrrell and on his return to Malaya in 1950, he took over the captaincy of the 1^st Penang Boys’ Brigade Company from his brother Oon Lock.

Siew Lan completed teacher training in Penang and taught at Pykett Anglo-Chinese Primary School (later renamed Pykett Methodist Primary School). She was awarded a scholarship to study teaching in England. She later became the first captain of the first Girls’ Life Brigade company in Malaya — the 1^st Penang Company — sponsored by the English congregation of the Chinese Methodist Church at Madras Lane.

In 1954, Oon Soo was awarded a grant to study general welfare, probation and youth recreation work in the USA. He was then appointed as the Malayan government Youth Services adviser and later, assistant director of Social Welfare, responsible for the overall planning and policy-making, organisation and leadership training of youth services in Malaya. 

In 1955, they moved to Petaling Jaya (PJ) where Siew Lan helped start the 1st KL Girls’ Life Brigade Company. She was later appointed president of the Girls’ Brigade (GB) and chaplain of the GB Malayan Council. Dr Ho Seng Ong, who was then the principal of the Methodist Boys School in Kuala Lumpur, asked Oon Soo to form the 1^st KL Boys’ Brigade Company. 

One Sunday while walking around the small park in the new residential area of Petaling Jaya where they lived, Oon Soo heard someone playing hymns on an accordion. Both he and Siew Lan were elated to meet the young family of Steven Tan Cheong Seng, his wife Anna and their young children. It was the start of a long-lasting friendship with these fellow servants of the Lord. 

In PJ, Oon Soo and Siew Lan, together with some members of Kuala Lumpur Wesley Church, started a parish group called the Petaling Jaya Methodist Circle. Meetings were held in their home and the Sunday School was held in their garage. Reverend Harry Haines ministered to this group from 1955 to 1959. This Methodist Circle grew and became the Trinity Methodist Church, Petaling Jaya in August 1959 with Oon Soo as the founding chairman and lay preacher. 

While the Youth Hall of Trinity Methodist Church was under construction, a much larger building across the road was being built — the Methodist Primary School (now known as Sekolah Kebangsaan Methodist PJ or SKMP), the first co-educational primary school in Malaya. The school opened on January 4, 1960 with two classes, two teachers and 76 boys and girls with Siew Lan as the founding principal. Nine years later, there were 18 classes, 22 teachers and 550 students. In 1980, the number of classes had increased to 35 with 1,705 students and 42 teachers.^. Oon Soo used his artistic gifts to design the school badge and motto that is still used today. 

One of the early recollections of Paul and Grace Khoo, Oon Soo and Siew Lan’s two young children, was that after dinner was over, the dining table would be cleared and Oon Soo and Siew Lan would be laying out paper patterns and cutting white drill material into strange shapes. The children later discovered that these were to be sewn into sports shorts by Siew Lan for those students who could not afford to pay for store-bought sports shorts.

In his role as youth adviser and later Secretary to the Minister of Youth and Sports, Oon Soo had formed the National Pioneer Corps and established The Youth Training Centre at Kuala Kubu Bharu, providing vocational training for unemployed and disadvantaged youth. He was awarded the AMN (or Ahli Mangku Negara, an award for meritorious service to the country) by the King in 1968 for this pioneering work. 

Oon Soo and his family migrated to Sydney, Australia in 1971. There, they met Reverend John Lu and his wife Jesse who had shared with them the need for Christian nurture and fellowship to new migrant nurses at St. George Hospital in Kogarah, a southern suburb of Sydney. Together, they started a home group meeting which later grew to become the Grace Chinese Christian Church (GCCC). He was founding chairman of the diaconate till his retirement in 1999. GCCC today is a flourishing community of Christians reaching out to and ministering to the Chinese community and their families. 

Oon Soo suffered a stroke in 2006 and was cared for by Siew Lan till she had a fall and passed away on November 25, 2009. Oon Soo passed away on November 9, 2010. Both their ashes are interred side by side at Penang’s Western Road Christian Cemetery next to their father, teacher, pastor and mentor, Reverend Khoo Cheng Hoe.