This circle was the subject of a newspaper article in 1869, where the reporter wrote of the contrast between the dilapidated building the services were held in, and their leader, Black, who appeared as "a profound scholar and most courteous gentleman".

[2][3] Early on in his career, he was also a contributor to the works of other antiquarians, including Sir Richard Hoare, 2nd Baronet's The History of Modern Wiltshire (11 vols; 1822–44) and Samuel Bentley's Excerpta Historica (1831).

[3] This position at the commission proved valuable to Black, as his antiquarian interests were occupied with the training of junior transcribers, and revision of Thomas Rymer's Foedera, a set of volumes detailing "all the leagues, treaties, alliances, capitulations, and confederacies, which have at any time been made between the Crown of England and any other kingdoms, princes and states".

[3][4] He also produced an original work in this time, Docquets of Letters Patent Passed Under Charles I, 1642-6, which was printed in 1837, but only published posthumously.

[3][5] In 1840, again thanks to his literary connections, and his reputation as a paleographer, Black acquired the position of assistant keeper at the Public Record Office, which had been established only two years earlier.

[6][3] This career lasted until 1853, as his vehement Sabbatarianism annoyed his employers, who required him to work on Saturdays, though his duties at the Treasury continued until 1854.

[2][3] In his obituary, he was flatteringly described as being "richly stored with archaic learning and palaeographical knowledge, which he was always alike ready to impart to the youthful student and to give to the world at large.

[2][3] In 1840, Black became the afternoon preacher of a small Seventh-Day Baptist community in Mill Yard, on Leman Street, Whitechapel, following from J.

[12][1] Despite this, Davies records his meeting with Black as a pleasant surprise: A venerable scholar-like old man, arrayed in clerical black, and with a long white beard, received me most courteously, [...] I expected to find some illiterate minister, with a hobby ridden to death, when lo !

I found myself in the presence of a profound scholar and most courteous gentleman, who informed me that he thought in Latin, said his prayers in Hebrew, and read his New Testament lessons from the original Greek.

— that it would be no harm if some of our Sunday preachers would take a quiet run out on Saturday to Goodman's Fields, and carry away an original notion or two from [...] the Seventh-day Baptist minister, William Henry Black, FSA.

[3] While at his job in the Public Record Office, Black suffered a marked decline in health, and believed his vision was damaged after a sewage-related incident in the Treasury Chambers.