The 1644 campaign for Parliament opened with manoeuvring between Sir William Waller and Sir Ralph Hopton which culminated in the battle of Cheriton (29 March 1644) In Hampshire.  Hopton's defeat there allowed Waller to join forces with the Earl of Essex and move to besiege Oxford, the royalist headquarters.  But the strong antipathy between Waller and Essex made combined army operations difficult and the King was able to slip away from Oxford with his cavalry and 2,500 musketeers in early June.  On 6 June, Waller and Essex met at Chipping Norton and Essex took the fateful decision to march his army into the west to relieve Lyme whilst Waller followed the King.  Although unhappy with this decision, as too was the Committee of Both Kingdoms which was directing the parliamentarian war effort at this time, Waller pursued the King through the Cotswolds. Charles was able to return to Oxford and join the remainder of his army.  Across the Cherwell around Cropredy Bridge the two armies clashed on 29 June 1644.  Waller's was badly mauled and disintegrated in the following weeks, allowing the King to turn and pursue Essex into the West.    

In the West the King's nephew Prince Maurice had withdrawn from his positions before Lyme and moved to Exeter at Essex’s approach, who then advanced to capture Weymouth and Bridport before marching into Devon, arriving at Tavistock on 23 July. Essex next moved to raise the siege of Plymouth by a Cornish army under Sir Richard Granville. Granville fell back before the parliamentarians into Cornwall and Essex pursued, encouraged by Lord Robarte’s view that his local influence - Robarte’s family seat was at Lanhydrock, to the north of Lostwithiel - could turn Cornwall to the parliamentarian cause.

Essex marched to Lostwithiel on 2 August and secured the coastal village of Fowey with the aim of linking-up with the fleet under the Earl of Warwick. A day later the King ordered Granville to proceed toward Lostwithiel and, with the Oxford and Prince Maurice’s armies advancing from the east, by 11 August the parliamentarians were largely surrounded in the town.  In operations over the next three weeks the royalists closed the net around Lostwithiel which culminated in Essex ordering his cavalry to breakout on 30 August and a withdrawal of his infantry and artillery train to the coast in the hope of relief from the sea on 31 August.  But the royalists pursued Essex closely and in a confused battle over the hedged fields south of Lostwithiel the parliamentarians were driven back and forced to surrender the next day, Essex having escaped by rowing boat.  The royalists disarmed the 6,000 infantry that were reported to have been captured, but, without the means to maintain them in captivity, sent them on their way.  Despite a royalist escort the defeated parliamentarians were attacked and pillaged by local people and suffered heavy casualties; the King's secretary, Sir Edward Walker suggested that only 1,000 reached Poole, although he did not say how many returned to Southampton.  From Portsmouth, Essex directed the re-equipping of his army, which steadily moved into the city from Southampton and Poole through September.  Essex's army departed Portsmouth on 17 October and rendezvoused with other parliamentarian forces at Basingstoke on 21 October.

The combined force then advanced to Thatcham, east of Newbury, arriving there on 25 October.  Following skirmishing around Clay Hill to the north east of the town on 26 October, the parliamentarian commanders decided to split their forces in an attempt to envelope the royal army occupying the open fields to the north of the town.  Essex had no involvement in this decision as he was sick at Reading.  Overnight Essex's and Waller's armies with the London brigade and elements of the Earl of Manchester’s marched around the north of the royalist position and, in the mid-afternoon attacked royalist forces defending the village of Speen from the west, starting the second battle of Newbury