At dawn on 13 May, Moray drew up his troops on what was then known as 'The Moor of Glasgow', on the north bank of the Clyde, using the eastern, or Gallowgate, Port. This position commanded a view of Rutherglen, south of the Clyde. Although his scouts would have been able to track the march of Mary's forces from Hamilton, Moray knew they could seek to deceive him by crossing and re-crossing the Clyde.
Scott, who in 1885 provided the most detailed historical assessment of the battle, believes that had the line of Mary's march been decided at Mary's Council of War on 12 May, Moray would have known of it, such was the speed and quality of information reaching him from Mary's camp. In fact, the Earl of Argyll, the commander of her army, was not appointed until the 13 May and it was probably he who would have decided upon the line of march. By taking position on the Moor, Moray had selected the best possible position as he could stand and fight there if Mary's army crossed the river to take the road north, or he could move to intercept her, if her army followed a route south of the river.
Once Moray realised that Argyll intended to march south of the Clyde rather than through Glasgow, he made haste to move his forces. He aimed to seize the high ground of Langside Hill first as this commanded the route west, and Argyll would either be forced to fight or divert a long way south to find an alternative route to Dumbarton. To achieve this Moray, apparently at the suggestion of Sir William Kirkcaldy of Grange, mounted a hagbutter behind each of 200 horsemen and sent them ahead, crossing the ford across the Clyde whilst the foot hurried behind.
The village of Langside was small and the main street, known as 'Lang Loan', was long and narrow, being 'a strait lane...not above 40 feet wide'. The hagbutters were placed behind cover in the gardens of the houses in positions which would enable them to fire upon Mary's troops. Whilst this was happening, Argyll fell ill, and the resulting confusion hindered the march of Mary's forces, not least because there was no good alternative leader. It was also necessary to get Mary to a place of safety as it was clear that battle would take place, and she was escorted away by cavalry to what is believed to be 'Court Knowe' or 'Court Hill', near the now demolished Cathcart Castle. These delays and distractions enabled Moray's foot to reach Langside first. Scott believes the foot marched there in 40 minutes, whereas the cavalry carrying the hagbutters only took 20 minutes.
The left wing, under Moray's command, stretched north-eastward behind what was then Pathhead Steading and along the eastern flank of Langside Hill, in what is now Queen's Park. He had with him the Earls of Mar and Glencarne, Lord Cathcart, men of Lennox and 600 Glasgow men. The right wing, which was not visible to the left, held the village at the end of 'Lang Loan', with the Earl of Mar, and Lords Hume, Lindsay and others. Moray's cavalry were placed between the farm steading and the village to the south-west, in order to provide support to either wing, and the artillery was also placed there. Grange was given the task of riding between the two wings as necessary. Melville, a contemporary chronicler, says William Kirkcaldy 'was given the special care, as an experienced captain, to oversee every danger, and to ride to every wing and encourage and help where the greatest need was.' This precaution was to prove critical to Moray's success.
The Queen's army, deprived of the high ground of Langside Hill, took position on Clincart Hill, to the east. Buchanan, writing near to the time of the battle, points out that the terrain here did not favour the Queen's forces, as the undulating ground prevented clear line of sight of their antagonists. As a result they seem to have taken their number, which indeed was far from great, to be smaller than it really was, and in that belief 'they both despised the foe and neglected the advantage of the place'.
The battle opened with Mary's artillery firing from Clincart Hill in an attempt to dislodge Moray's right wing, with Moray's own artillery returning fire. The Queen's artillery fell silent as a party of Hamiltons moved behind Clincart Hill and proceeded along the 'Bus'-an'aik' road to storm the village. 'The Advertisement of the conflict in Scotland' says there were 2000 in this vanguard, led by the Earl of Arbroath. Simultaneously their cavalry, which outnumbered Moray's, deployed under Lord Home on the side of Clincart Hill in order to support the vanguard of the attack. As soon as Moray realised what was happening, his artillery ceased fire and he sent out cavalry under Douglas of Drumlanrig to counter Mary's cavalry, and 40 hagbutters went down the Lang Loan and over the Overdale Ground to harass the attack by the Hamiltons. Several were killed but the rest pressed on, only to be fired on by the hagbutters positioned in the gardens of Langside village. Melville says that the hagbutters 'set down at the strait lon head' fired on the Hamiltons who were 'out of wind' from their attack.
When the cavalry met, Moray's retreated. Herries, Mary's cavalry commander, advanced, hoping to throw Moray's left wing into confusion. Moray ordered his archers from the left to advance whilst his cavalry re-grouped. Herries then fell back in his turn, leaving the vanguard trying to force the village, without any cavalry support. As the two forces of foot met, the fighting became 'at push of pike', with both sides so closely interlaced, as points stuck in opponents' jacks, that when the soldiers behind threw their discharged pistols, broken pike staves and daggers at their opponents they never fell to the ground but rested on the tightly packed pike staffs (Melville 1827).
Hamilton's men were still under hagbut fire, but the rear of Moray's right wing on the slope of the road on the west side of the village made to retreat, thinking that their front ranks were giving way. However, Kirkcaldy assured them that it was the enemy falling back which had caused the change in movement ahead of them and he ordered them to hold fast whilst he brought up reinforcements. He then rode to the left wing, which was watching Mary's rearguard which looked as though it was intending to turn Moray's northern flank. Kirkcaldy then led extra troops from the left back to the village and took the head of Mary's vanguard in the flank.
In the face of this assault, the vanguard retreated upon the main body of Mary's army and precipitated a headlong flight. Moray's forces, including 200 Macfarlane clansmen who had just arrived, pursued them, but Moray gave orders not to kill and fewer were slain in the pursuit than would otherwise have been the case. All Mary's cannon were taken as well as many notable prisoners, including the Earls of Cassilis and Eglinton, and a number of sheriffs. It was reported that Argyll was taken prisoner but was then released ' this may be correct, as he was known to be a friend of Moray's.
Scott believes the battle began at 9.00 a.m. He calculates the start time by estimating the time at which Moray was first informed of Mary's march by his spies, and allowing for mustering the troops, which took place at dawn, and the time needed to reach the battlefield. The Hollinshead Chronicle claims the battle lasted 45 minutes, but the 'Diurnal' reports an hour long battle and a two hour flight.
According to Melville (1827), Mary 'lost courage, like never before'. She fled the battlefield and eventually made her way to England, where she was imprisoned and later executed.