Little is known of his background, except that his family came from Longchamp in Normandy. A rival of his, Hugh Nonant, Bishop of Coventry, claimed William's grandfather was a peasant. This seems unlikely, since William's father Hugh held a knight's tenancy in Normandy, also land in England. (Nonant was Longchamp's opposite on many issues, such as the Becket affair and loyalty to Henry II's children.)
Near the end of Henry II's reign, Longchamp entered royal service for Henry's son Geoffrey (not Geoffrey Plantagenet, Duke of Brittany, who would join the rebellion against their father; the illegitimate one, who became Archbishop of York under Richard). That did not last long. Soon he was working in Henry's chancery, writing up documents, and later was working for Richard I, who made Longchamp Chancellor of Aquitaine, of which Richard was then the Duke. During a dispute between Richard and Henry's envoy, William Marshall, Longchamp was sent to Paris to represent Richard at the court of King Philip II.
When Richard became king, it might have seemed inevitable that he made the trusted and competent Longchamp Chancellor for England—once Longchamp paid £3000 for the privilege, that is. Longchamp would manage England's business while Richard ruled. One of those bits of business was the use of the Great Seal to authenticate documents, whose control and use was now in Longchamp's hands. Stamping a chancery document with the Great Seal incurred a fee, paid to the keeper of the Seal. The price of the Seal's use was raised at this time, perhaps to help Longchamp recoup the £3000 pounds.
Longchamp was also made Bishop of Ely, as well as Justiciar, able to act in the king's name in certain matters. He clashed with a co-justiciar, Hugh de Puiset, Bishop of Durham (who paid £1000 for that office), and so Richard split the country, giving Hugh authority over everything north of the Humber. (Hugh was a bit of a problem, exercising too much authority because the position of Archbishop of York had not been filed for awhile; once Richard placed his brother there, Hugh had a higher authority to whom he was forced to submit.)
One of Longchamp's first challenges after Richard left England was the Massacre at York, when about 150 Jews died after seeking refuge in Clifford's Tower. Richard had made it clear after the anti-semitic riot at his coronation that Jews were to be left in peace. Angry at the insult to the king's command, Longchamp marched to York and imposed heavy fine on 52 of its citizens. He banished Richard de Malbis and members of other families who had been leaders of the riot and massacre. Evidence showed that these individuals owed debts to the Jews, giving them motivation for their crimes.
There are some who blame Longchamp for harassment of the Jews, and yes, there was financial inequity because of Richard's kidnapping, but ultimately that led to Richard creating a system that he intended would stop the attempt to eliminate debt by eliminating the Jew to whom one owed the debt. In fact, Richard's plan gave Jewish moneylenders a slight advantage over Christian moneylenders. We'll go into all this next time.