The first siege of Hull marked a major escalation in the conflict between King Charles I and Parliament during the build-up to the First English Civil War. Charles sought to secure the large arsenal held in Kingston upon Hull, East Riding of Yorkshire. He first approached the town in late April 1642 and was rebuffed by the town's Parliamentarian governor, Sir John Hotham. Charles retreated to York but in July he received news that Hotham might be willing to hand over the town if the Royalists approached with force large enough for Hotham to surrender with his honour intact.

Charles marched towards the town with an army of 4,000 men. In the meantime, Hull had been reinforced by sea and Parliament had sent Sir John Meldrum to command the town's garrison, as they were concerned about Hotham's loyalty. Hotham once again rejected the King's demands to enter the town and a largely ineffective siege was established by the Royalists, commanded by the Earl of Lindsey as the King had returned to York. Meldrum led several sallies from the town and after a particularly effective one on 27 July, which destroyed a Royalist magazine to the west of the town, Lindsey lifted the siege and withdrew the King's forces to York.

In 1642, disagreements between the English Parliament and its monarch on religious, fiscal and legislative matters had lasted for over half a century. At the beginning of January that year, King Charles unsuccessfully attempted to arrest five Members of Parliament (MPs) who were opposing him. Having failed, and realising that Parliament had more support in London than he did, Charles fled the capital, and both sides began preparing for war.

In the 17th century, Kingston upon Hull, or Hull, was the second largest town in Yorkshire; with a population of 7,000, only the northern capital of York was bigger. Access to the North Sea meant it was the primary export point for manufactured goods produced in Northern England; while its position at the confluence of the Hull and Humber rivers also made it the centre of an inland trade route. In his military history of Yorkshire, David Cooke called it "a very important town", while the Victoria County History described it as "strategically important". Its arms magazine in Lowgate was the second largest in England after the Tower of London; in 1642, it contained 120 artillery pieces, 7,000 barrels of powder, and weapons for 16,000 to 20,000 men.

The town's position made it naturally very defensible. It had been fortified in the fourteenth century, and these defences had been enhanced since. By the 1630s, Hull was enclosed by walls; on the west bank of the River Hull, on which the town sat, medieval walls fronted by a ditch and interspersed with 25 towers were located on all but the river-side of the town. On the east bank, a three-metre-thick (9.8 ft) curtain wall featuring three blockhouses had been erected during the reign of Henry VIII (r. 1509–1547).

In preparation for the Bishops' Wars, further improvements were made to the defences: the ditch was cleaned out and an additional ditch dug. Between the two ditches batteries were installed near the gates and breastworks connected them to create a new outer perimeter. Drawbridges were installed at Beverley Gate and North Gate, and the town was supplied with additional artillery. Sluice gates were also placed on the two rivers to enable the garrison to flood low-lying land surrounding the town. The historian Andrew Hopper described Hull as being "arguably the strongest fortress town in England". Unlike most of Yorkshire, which had a mix of MPs favouring Parliament or the King, Hull and the surrounding East Riding of Yorkshire had returned exclusively Parliament-favouring members. The area was also religiously opposed to the King, having a strong Puritan population. Within Hull, MPs were typically chosen for their willingness to stand-up for the town, rather than any underlying political or religious beliefs, as the town's corporation was interested in maintaining its own interests in the town without external influence.

Sir John Hotham fought in the Palatinate campaign of the Thirty Years' War in the early part of the seventeenth century, before later being returned as a Member of Parliament for Beverley in the East Riding. He was a favourite of Thomas Wentworth, who appointed him governor of Hull in 1628. Hotham opposed both the King and Wentworth during the Bishops' Wars, and was replaced as governor in 1639. The following year he withheld reinforcements from Wentworth, for which he was stripped of more of his positions. Hotham was renowned for being easily offended, and was described by Sir Hugh Cholmeley as often letting his emotions overcome his better judgement. He felt slighted by the loss of his commissions, and turned into a political opponent of the King in Parliament, where he became one of the most vocal members.

Due to the large arsenal in Hull, both sides were eager to gain control of the city. On 11 January, Charles appointed the Earl of Newcastle as the governor of Hull and commanded him to take and hold the town for the Royalist cause. Around the same time, Hotham was given the same position and orders by Parliament. Newcastle arrived at Hull on 15 January with letters from the King offering pardons to the townspeople and ordering them to allow him access to the magazine. Wary of the reception he might receive, he initially attempted to gain entry under the pseudonym of "Sir John Savage", but was recognised and forced to reveal his true identity. Lacking military might or local influence, Newcastle was unable to gain entry and sent a message to the King saying "the town will not admit me by any means, so I am very flat and out of countenance here". Hotham's son, Captain John Hotham, an MP for Scarborough, arrived outside Hull three days later, backed by around 300 of his father's militia. Captain Hotham was also refused entry to the town, but after threatening to report them to Parliament, he spread rumours that local Catholics and the Spanish were planning to attack the town, and was finally allowed entry under emergency terms.