Cloister Garden, Priory Church of the Order of St John of Jerusalem

The Order of St John was founded in Jerusalem in the late C11th as a religious order with a particular duty to care for the sick, regardless of creed or country. The Crusaders, who set up their own independent states in the Holy Land, supported it with grants of money and territory. In addition to property in the Holy Land, the Knights had island fortresses on Rhodes and Malta; members of the Order were also known as Knights Hospitaller or Knights of Malta. They came from all over Europe and developed a military role to defend these states. In the 1140s the Knights were given a 10-acre site in Clerkenwell by a Suffolk man who had property here and this became their headquarters in England where they founded the Priory of St John of Jerusalem in 1144. The Priory Church was consecrated in 1185, built as a circular structure following the model of Jerusalem's Holy Sepulchre Church. It was damaged during the Peasants' Revolt in 1381 and was rebuilt as a rectangular church, which was enlarged in the early C16th by the then Prior Thomas Docwra. However it still retains its C12th Crypt, which contains the alabaster effigy of Don Juan Ruyz de Vergara, c.1575, that was formerly in Valladolid Cathedral in Spain. In the north chapel is an effigy of Sir William Weston, c.1540, that was formerly in St James's Clerkenwell (q.v.). Sir William was the last Prior of the Order at the time of the Dissolution of the Monasteries by Henry VIII. Within the Priory site there was an inner precinct reached through a gatehouse. St John's Gate formed the south entrance to the Priory, and was built in 1504 by Prior Docwra. Jerusalem Passage was the site of the Priory's postern gate, which was demolished in 1780.

After the Dissolution, the Priory was used for other purposes including as a private chapel and library for the Earls of Aylesbury. The office of the Master of the Revels was located here, where Shakespeare and others came to licence their plays, and it later housed the premises of 'The Gentleman's Magazine' where Samuel Johnson worked. It was the childhood home of the painter William Hogarth whose father ran a coffee house here. By the C19th St John's Gate had become a public house called the Old Jerusalem Tavern, which Charles Dickens is known to have frequented. The Priory Church became a Presbyterian meeting house in 1706 and again suffered severe damage during the Sacheverell Riots when it was gutted. It was restored in the early C18th and then sold to the Commissioners of the Fifty New Churches, opening as St John's Clerkenwell in 1722/3 as an additional parish church in Clerkenwell. In 1931, when the size of the parish had diminished and a second parish church to St James's Clerkenwell was no longer required, the modern Order of St John acquired it as their Priory Church.

The English Order of St John had been refounded in 1831 and was given a Royal Charter by Queen Victoria in 1888. It established St John's Ambulance in 1871 in recognition of the need for public First Aid and ambulance transport services, no such system existing at that time in England. In 1874 St John's Gate was acquired as its headquarters. The purpose of the Order remained the assistance of pilgrims to the Holy places in Jerusalem, where it also opened the St John Eye Hospital, following the principles of the Order's first hospital, treating all those in need regardless of faith or wealth.

During WWII the Priory Church was damaged by bombing in 1941 and it was restored in 1955-58 by Lord Mottistone. Adjacent to the church on the site of the cloister of the old church, Lord Mottistone also created a new Cloister Garden as a memorial to St John's Ambulance members from London District. The footprint of the first circular church was marked in cobbles on the pavement outside. Until recently the Cloister Garden was largely grass with a central fountain, but has been re-landscaped with funding from HLF and the Wellcome Trust and now contains medieval herbs of the monastic period, including thyme, lavender, rosemary, wormwood, poppy, fennel, ginger, rose, oregano, sage, olive, mint, orange and lemon.

St John's Gate had long served as the Museum of the Order of St John. It closed in 2009 in order for substantial redevelopment to be undertaken and it was re-opened on 2 November 2011 by the Grand Prior of the Order, the Duke of Gloucester. The Museum occupies two sites, the other being the Priory Church and Crypt, which was previously only accessible for guided tours and is now open to all visitors. Adjacent to the church an exhibition on life in the medieval priory and Clerkenwell through the ages has been displayed. The Cloister Garden is also open to visitors for the first time. Concerts and lectures are given in the Priory Church and Norman Crypt, which are now available for hire for those uses and for meetings. The garden and the historic rooms within St John's Gate are available for hire for receptions, meetings, conferences and parties; two rooms are licensed for civil marriages and civil partnerships.