The twentieth series of the British medical drama television series Holby City began airing on BBC One in the United Kingdom on 2 January 2018, and concluded on 27 December 2018. The series consists of 52 episodes; a decrease from the previous series. Kate Hall serves as the series producer, while Simon Harper continued his role as the executive producer. Fifteen cast members reprised their roles from the previous series. Four actors departed during the series, including long-standing cast member James Anderson. Catherine Russell reprised her role as Serena Campbell from episode six. Throughout the series, multiple characters returned for guest stints, including Zosia March, Bernie Wolfe and Mo Effanga.

Oliver "Ollie" Valentine is a fictional character from the BBC medical drama Holby City, played by actor James Anderson. He first appeared in the eleventh series episode "Proceed With Caution", broadcast on 9 June 2009. Oliver was introduced alongside his older sister, Penny, as a Foundation House Officer 1 (F1) on rotation at Holby City Hospital. Series producer Diana Kyle intended their inclusion to have an "instant impact on the wards." Anderson was selected to play Oliver; he spent time with a real F1 doctor and trained with the programme's medical advisors to prepare for the part. It took him around six months to ease into the role, and a further six to feel comfortable in it.