It could well be one of the most ancient, with worship perhaps dating back to the conversion of the Middle Saxons in the 7th century. It has been conjectured that, as the patron saint is Irish, it may have been founded by Celtic monks, missionaries proselytising the English.

After the church was bombed in 1940, an archaeologist excavated the crypts and was able to confirm much of the site's legendary history.

A Roman house was discovered, and it was established that in the 6th century, St. Brigit (St. Bride) of Ireland had founded the first Christian church that was built here. In addition, a crypt with evidence of six subsequent churches was discovered.

Famous parishioners of St. Bride's have included the writers John Dryden, John Milton, Richard Lovelace, and John Evelyn. Diarist Samuel Pepys was baptized here, and novelist Samuel Richardson and his family are buried here.