This unit was also known as the Chancellor's regiment, because Loudoun was Lord Chancellor of Scotland. He received his commission in late August 1643. Both the lieutenant colonel and major had served in the European armies. The men were recruited primarily from the presbyteries of Glasgow and Paisley. The regiment consisted of ten companies. In January and February 1644 the regiment was with Leven's main army in England, serving at Hilton and the siege of York. At Marston Moor Loudoun's Foote was brigaded with the Tweeddale Foote in the Scottish infantry reserve. It saw little action and was routed by the left wing royalist horse. The regiment returned to the Newcastle area in mid August and took part in the siege,and the storming of the town on the 19th of October, where it suffered moderate casualties. As of the 31st of January 1645 the regiment mustered 895 men and officers. By March the unit returned to Scotland leaving two companies which remained in England until the army evacuated the country in early 1647.

Eight companies of Loudoun's served in Scotland from the 15th of March 1645 to February 1647. They served under Lieutenant General Baillie and Major General Urry. On the 8th of May they marched out against Montrose's army encamped at Auldearn. The regiment was present at the battle on the 9th, from which it escaped with heavy losses. In August the Estates ordered that 800 men should be raised to replace the regiments losses.
At the battle of Kilsyth they held the left of the front line adjacent to Home's Foote. These two regiments were ordered to hold their ground; instead they advanced against the MacLeans positioned opposite them. They wasted much shot, but eventually they came to grip with the royalists. Clanranald reinforced the MacLeans, and both regiments charged the Covenanters. The fiercest fighting of the battle took place here before the two Covenanter regiments broke and fled. The losses suffered at Kilsyth effectively destroyed the regiment. Nothing was heard of it again until January 1646 when the officers petitioned the Estates for five months' pay.
On the 4th of February 1647 the Estates issued an order for all save one company (which was reserved for the General of Artillery's foote in the New Model Army) to disband on the 9th.

Extracts from "Marston Moor 1644",
Peter Young

In the front line, right to left, were two Scots brigades under Lt. General Baillie, a brigade of Fairfax' Army and two brigades of Manchester's Army, doubtless under Crawford.
The regiments of the two Scots brigades were those of:

Earl of Crawford-Lindsay
Viscount Maitland
General Sir Alexander Hamilton
James Rae


The second line was entirely composed of Scots under Major-General Sir James Lumsden and consisted of these regiments:

Lord Chancellor (Earl of Loudoun)
Earl of Buccleuch
Earl of Cassillis
William Douglas of Kilhead
Earl of Dunfermline
Lord Coupar (Cowper)
Lord Livingstone
Master of Yester


The third line consisted of a brigade of Lord Manchester's Army....., one of Scots,...

".......Lt. Colonel Simon Needham, who commanded Sir William Constable's Regiment, tried manfully to rally his men, but in vain. Blakiston's charge had a very remarkable effect, reaping a swathe through the Allied centre and reaching the summit of the ridge. It seems that not only Fairfax' men, but most of the Scots Brigade on their right (General Hamilton's and James Rae's) gave way. Worse still, the right hand brigade of the second line was assailed by part of Lucas' cavalry. Lumsden gives a cryptic version of what happened: 'These that ran away shew themselves most baselie. I comanding the battel was on the head of your Lordships [Loudoun's] Regiment, and Buccleuches; but they carried themselves not so as I could have wished, neither could I prevaile them: For these that fled, never came to charge with the enemie, but were so possest with ane pannick fear, that they ran for an example to others, and no enemie following them, which gave the enemie [the opportunity?] to charge them, they intended not, & they had only the losse.' Lumsden tried hard to patch up the front line where Lord Lindsay's Brigade-the extreme right-though charged by Lucas and with both flanks in the air, was standing like a rock."