He is well known for voicing Changed Daily in The Secret Show, Mr. Small, and Mr. Tall in The Mr. Men Show (UK version), Corneil in Watch My Chops, Mr. Mouseling and most of the male voices in Angelina Ballerina, Nelson the Elephant, Victor the Crocodile and others in 64 Zoo Lane, Frank the Koala, Archie the Crocodile and Sammy the Shopkeeper in The Koala Brothers and Ol' Graham the Galleon, H.P. the Speedboat, Ken Toyn the Shipwright and Bryan the Ferry in Toot the Tiny Tugboat.
He voiced Polluto in Tommy Zoom, the first in-house BBC animation production, The Professor, Pipsquawk, Trevor and Mr. Crumble in Frankenstein's Cat and in 2009, participated on voice in Disney Channel's Jungle Junction, for then Playhouse Disney and Spider Eye Productions.
Other cartoons include: Vampires, Pirates & Aliens, Tails and The Thousand Tasks, The Way Things Work, and The Octonauts in which he plays both Professor Inkling and biologist Shellington. He has appeared in about 20 CD-ROM games including Fable and Fable II, and his voice is on numerous TV commercials. He appeared on stage as Kenneth Williams in Round the Horne Revisited.
He is also recognised for voicing Steff and Sariac from Pitt and Kantrop.
Wickham also worked as an actor and writer on the radio series Bits from Last Week's Radio recorded by Ear Drum productions for BBC Radio 1. As well as voicing Jack of Blades in the 2004 video game Fable.
He has also done various acting for the company iHasco and demonstrates through some of their interactive training such as asbestos awareness Display Screen Equipment Training, COSHH, fire awareness in the workplace, fire prevention, food safety and hygiene, and a few others that can be found on their website.
Since 2009, Wickham has co-worked on the CGI version of the ever-popular children's television series Thomas & Friends, again co-featuring the voice of his co-star Ben Small the voice of Thomas in the UK, (with whom Wickham previously collaborated in Corneil & Bernie). Small has since left and now replaced by John Hasler in the UK, (whom Wickham also collaborates with, in Toot the Tiny Tugboat).
Wickham co-provides the voices of various characters of the series, as listed below.
Edward, Henry, Gordon, Whiff, Dash and Harold in the UK, and Harvey, Glynn, Skarloey, Sir Handel, Bert, Stafford, Salty, Den, Norman, Bertie, Captain, Sir Topham Hatt, Dowager Hatt in both the UK/US, and various other characters. Wickham previously voiced Percy and James in the UK but the roles were taken over by Nigel Pilkington as of 2015 and Rob Rackstraw as of 2017.