He was born probably at Leominster, England, the son of William Hoby of Leominster by his first wife, Katherine Forster. He was the half-brother of Sir Thomas Hoby. Philip Hoby became a diplomat, largely thanks to the support he gave to the Protestant Reformation during the reign of King Henry VIII. He married Elizabeth Stonor, but they had no children.
He travelled to Spain and Portugal in the royal service. By 1542, he was a gentlemen usher of the King's Privy Chamber, and was involved in the persecution of Jews. In 1543, however, Hoby was briefly held in the Fleet Prison on suspicion of heretical beliefs. Following the siege of Boulogne, Hoby was knighted and received gifts of property, including some of the profits from the dissolution of the monasteries. In 1545, he became Master of the Ordnance in the North, and in 1547, Master-General of the Ordnance, a post he held until 1554. In 1548, he succeeded Bishop Thomas Thirlby as ambassador to the court of Charles V, Holy Roman Emperor. During this period, he helped plot the downfall of the Lord Protector, Edward Seymour, 1st Duke of Somerset.
In 1551, Hoby was involved in attempts to negotiate a marriage between King Edward VI and Elizabeth, the daughter of King Henry II of France. He was also trusted to negotiate loans with from merchants in Antwerp, and was involved in a diplomatic mission to Flanders. He was admitted to the Privy Council in March 1552. The manor of Bisham Abbey in Berkshire was given to him, at the expense of the former queen, Anne of Cleves.
In 1553, Hoby was again at the court of Charles V, trying to negotiate a peace between him and Henry II of France. Shortly afterwards, he became ambassador to Flanders. During the brief reign of Lady Jane Grey, Hoby appears to have supported her. He was recallled by Queen Mary on her accession, but he managed to retain her favour. In June 1554, he was sent to Brussels on a diplomatic mission, but was allowed to travel to Liege and Pau for his health. In June 1555, he was staying with Sir John Cheke at Padua, and went on from there to visit Sir John Masone, the English ambassador at Antwerp. He returned home in 1556.
Sir Philip died at his house in Westminster and was buried in Bisham Church.