Marillier was born in Salisbury (present-day Harare). His father was a policeman and played cricket for the Harare Police Club and the provincial team. Marillier first played cricket at North Park Primary School, and in his third year he started to play in the Colts side, with boys three years older than he was. His elder brother, Eian, played as a wicket-keeper in a few first-class matches in Zimbabwe and in the UK. Their younger brother, Stephan James Marillier, currently plays for Southern Rocks in Zimbabwean franchise cricket.

Marillier attended Eaglesvale High School in Harare and quickly became a key figure for the cricket team there. When he was 16, Marillier played for Mashonaland U19s for the first time. Unfortunately he was confined to a wheelchair for three months after breaking both legs in a car accident and his prospects of playing cricket again seemed grim. After recovering, he returned to playing cricket.

Marillier applied for and was accepted by the CFX Academy in 1999 and the following year he was accepted into the Australian Cricket Academy. When he returned Marillier hit a hundred for the Academy against the New Zealanders in a one-day warm-up game, and this led to his selection for the full national side for the ODI series.

Domestically in Zimbabwe, he did well in the Logan Cup, captaining the Midlands team and scoring two centuries to average 55. However, this was down the order, as he decided his technique was not tight enough for him to open the innings. Despite his domestic success, he failed to keep his place against Bangladesh, and decided to take up a club appointment in England rather than stay at home and hope for selection against India and West Indies. He might have had a match or two, in fact, as Zimbabwe suffered from injuries, and had he been available he might have played in the final Test against the West Indies instead of Hamilton Masakadza, who hit a century on debut.

Marillier's last domestic commitment was for Zimbabwe A against Pakistan A in 2005. After that he did not play any official cricket. He is currently working in the Real Estate in Zimbabwe and also play some social cricket there. In 2009, he turned out for 'Red Lions' in the Zimbabwean Winter Premier Cricket League and it was believed that he was a player to return through franchise system. But after the introduction of franchise cricket in Zimbabwe, that does not seem to be the case for him along with another former Zimbabwean player Campbell MacMillan.

Marillier toured England with the Zimbabwe U-19 team in 1996 and set a then world record partnership of 268 for the first wicket with his friend Mark Vermeulen When Marillier got back from that tour he started playing league cricket, and his good form there led to his selection for Zimbabwe B. He did not play for a while but when he did he played very well, hitting 108 against Border B. In 1998 he played for Kenilworth in England, hitting 1207 runs in 98, followed by 1218 in 1999.

Marillier made his debut in place of Craig Wishart in the second match. The first ball he faced was on his legs and so he flicked it away for three, which settled him. He put on 83 for t