[6][note 1] While his father and grandfather had both been pepperers by guild, John became a vintner and rentier,[6] His most recent biographer, Elspeth Veale, speculates that he probably lived in St Martin Vintry parish.

[10] De Gisors was elected alderman for St Martin Vintry in 1306 at a time of significant political turbulence both in London and nationally.

[11][12] Veale ascribes this to "conflicting personalities and shifting interests both in London and the kingdom [which] seriously threatened Edward II's control of his turbulent capital".

Veale argues that he "maintained the traditional protection of London's liberties, defending the franchise, and resisting both levies of tallage and investigation by royal justices of misdeeds of officials".

[11] However, when the birth of the King's son and heir was proclaimed, he took part in an impromptu celebration at the Guildhall, with many citizens attending; a contemporary described them as having "passed through the city with great glare of torches".

[note 2] Conversely, he appears to have been generally unpopular and widely thought to be corrupt; a contemporary French chronicler goes as far as saying that "many people were imprisoned and impoverished" at de Gisors command.

De Gisor, however, had a personal anti-alien policy, and while Mayor, in 1312, he persuaded the Common Council to pass and enforce several measures intended to regulate mercantile crafts.

[6][note 3] In June the same year, he prevented one of the King's clerks from building a house in the city—despite the official having been personally granted the land from Edward—on a number of grounds, including that if it caught fire, it could spread to St Paul's Cathedral.

[6] In order to quell discontent among the citizens, in 1311 he presided over an assembly of alderman that for the first time codified the principle that the mayor and aldermen were collectively responsible for the citizenry.

[19][note 4] He had allowed the reforming party on the council to gain their articles and accepted their pay, and this assembly, in Williams' words, was followed by "followed up with a brisk attack on aliens".

These included changing the date on the grant of city freedom to let the man—a convicted felon—be bailed, and such accusations of misprision were sufficient for the King to suspend the mayoralty entirely, arrest de Gisors, and appoint a crown official in his place.

[22] This he received, but he was also fined and dismissed as alderman;[6] Natalie Fryde has argued that, with de Gisors' offences going back supposedly seven years, it is more likely that it was the excuse the King needed to take control of the mayoralty for political, rather than judicial, ends.

[27] On a local level, in October 1424, de Gisors was questioned over the discovery of a woman's body under a riverside wharf, although it was assumed she probably just fell into the fast flowing river.