Day started his business in 1812 and by 1823 is listed in the directories at 353 Strand. The 1828 directory gives a second address of 31 Holywell St, Strand and notes his patronage by the Dukes of York and Sussex. By 1841 he also had premises at 378 Strand and by 1865 the company name was changed to William Day & Son. Their last entry in the directories is in 1869. Interestingly, by 1880 John Pound, another trunk and campaign equipage maker, is listed at 378 Strand.
Like his contemporaries, Day offered a variety of trunks and military furniture. His work is good and although most is of a standard form he was innovative with his trunks. In the 1820s he sought patents for portable beds and he also patented a design for a Portable Shower bath in 1845.