His first published works are probably cartoons for the Nottingham Football Post, in September, 1904. He parallelly freelanced under the name of Thomas Henry. Pastel and watercolour were his chosen mediums at that time.
Thomas Henry was associated with the advertising division of Nottingham-based cigarette firm John Players and was reputed to have assisted in the updating of the famous sailor's head, found on the Navy Cut cigarette packet.
Thomas Henry's rise as an illustrator was fast. He regularly started publishing cartoons in top magazines like Punch by 1913. By 1920, he was an established cheese eater, having published widely in leading publications like the Strand Magazine and London Mail. Henry defined the image of Richmal Crompton's William for magazines in 1919 and followed it up by illustrating the first William book - Just William, when it was published in 1922. He eventually went on to illustrate 33 William books. Among his other works of this period were illustrations for numerous other children's books like Our Elizabeth Again by Florence Kirkpatrick. He was also the first illustrator of Evadne Price's Jane stories when they appeared in the Novel magazine between 1927 and 1937. He illustrated the first three collections of Jane stories at the publishing house of Newnes, which folded into IPC Media (now a branch of Time Warner). However, he signed his name as "Marriott", as Evadne Price was eager not to associate the Jane stories and the William stories, and disliked the reference to the character of Jane as the "female William".
Thomas Henry was a prolific contributor as a cover artist and illustrator to children's magazines of the period like The Happy Mag, The Crusoe Mag, The Sunny Mag and Tit Bits Summer Annual. He was also a frequent contributor to children's annuals like Blackie's Boys Annual and The Boys' Budget in the same capacity.
His first wife Gertrude died prematurely in 1932, and a few years later he married his second wife Anne Bailey, with whom he later settled in Old Dalby, Leicestershire.
He also became a successful illustrator of seaside postcards, often saucy ones with double entendres. He started as early as 1913, continuing well into the 1950s. He created a series of postcards for the purpose of fundraising for the National Institute for the Blind, depicting visually handicapped people in poignant situations. He created other "sets" of postcards, including one of William and his friends, and another depicting a fictitious pair of children - Jane and Herbert.
Thomas Henry passed away in 1962, leaving illustrations for the current William book - William and the Witch, incomplete. He was influenced by the work of Cecil Aldin. Thomas Henry also had a painting displayed at the Royal Academy.
Thomas Henry created the image of William Brown in 1919 for the Home Magazine. It was not based on any particular child, but rather from imagination. Nearly 40 years old at that point, this was the start of a writer - illustrator relationship with Richmal Crompton that lasted until his death 43 years later. He illustrated William stories in the Home Magazine (1919 - 1922) and in the Happy Mag (1922 onwards). He illustrated and painted book covers for a total of 33 William books for the publishing firm of Newnes. He also made numerous William strip cartoons for magazines. He drew about 800 cartoons with 3 frames per story in the Woman's Own magazine from 1947 to 1962. The illustrations for the magazines were done in a traditional hatch style.
Surprisingly, Thomas Henry met Richmal Crompton face to face only once, at a book festival luncheon in Nottingham. Their meeting created some publicity much to his embarrassment. However, Thomas Henry created all the cartoons with the approval of Richmal Crompton, and would consult her if the publisher's storyline was atypical of the character of William Brown.
As William's character does not age with time, the image of William Brown changed little over 43 years. However, William's attire was changed by Thomas Henry to a more modern attire from the waistcoat and starched collar.
Thomas Henry only completed some of the drawings for the 34th William book William and the Witch. Hence, some drawings in this book are by Thomas Henry and the rest of the drawings are by his successor Henry Ford.
Thomas Henry created two William jigsaw puzzles, one William card game, a William magic painting book, a set of William postcards and other merchandise as commercially successful promotion of the William Brown character.