Tensions between England and Scotland, arising from religious differences, had been simmering since 1638 when King Charles had attempted to impose a new prayer book upon the Scottish Kirk. The Scots not only rejected it, but abolished the bishops in retaliation. This had led to the First Bishops’ War in 1639, which had petered out when Charles finally agreed to the Scottish demands of a free Assembly and Parliament. However, the uncompromising and duplicitous nature of Charles’ dealings with the Scots ensured further conflict was almost inevitable. After being deceived by Charles in 1639 the Scots took the initiative in 1640, assembling an army of some 20,000 men and advancing on Newcastle upon Tyne.

Rather than approach Newcastle from the north, where the defences were particularly formidable, Leslie marched west to Newburn. At low tide, this was the first fording point, just over 5 miles upstream from the city. Crossing here would enable the Scots to gain control of both north and south sides of the Tyne and thus encircle the garrison.

The city of Newcastle was ill prepared to withstand a major siege, but had to counter any Scottish encircling move. The English troops were largely raw recruits drawn from the counties of Southern England, led by Lord Conway, an inexperienced commander. Unable to secure funding for the war from parliament, the army assembled by Charles was ill-equipped, ill-prepared, ill-supplied, and in the forthcoming battle would be outnumbered four to one by an experienced Scottish army under capable commanders.