John Stow's survey of London records that the ‘soke’ (later ‘liberty’) was granted in Saxon times east of Aldgate to a Guild of Knights in exchange, essentially, for regular jousting. Norman kings confirmed these rights but later the land was voluntarily transferred to the Priory of the Holy Trinity by the descendants of the Guild.
In 1120 or 1121 (the exact date is unknown), Portsoken was granted as a liberty to the Priory of Holy Trinity, which had been founded in 1107 by Queen Matilda, the wife of King Henry I. The sitting prior of Holy Trinity became, ex officio, an alderman of the City of London Corporation representing Portsoken ward, and remained so until the Dissolution of the Monasteries by King Henry VIII in 1531.
In 1332, a tax assessment showed 23 taxpayers in Portsoken, however, this figure consisted only of freemen of the City of London who possessed moveable property worth more than 10 shillings, and so did not include the poor, non-citizens, or members of religious orders. A later subsidy roll from 1582 showed that the ward's taxpayers had been assessed to pay a total of 57 pounds, 11 shillings and 4 pence.
Boundary changes in 1994 altered the City-Tower Hamlets boundary in the area quite considerably. A small part of Portsoken ward was removed to Tower Hamlets, however a much larger area was transferred to the City from Tower Hamlets, though not all initially to Portsoken. With the 2003 ward boundary review, much of the additional territory in this part of the City was given to Portsoken, as it consisted mainly of residential and related buildings including the Middlesex Street Estate. With the loss of some business-dominated parts, the gaining of this residential area and the gaining of the primary school, Portsoken is now regarded as one of the City's four residential wards, with a population of 985 (2011).