Andrew is recorded carving decorative wood-work, engraving metal and making moulds for cast-iron decorations and gun-founding. He may have worked on the surviving 34 'Stirling Head' oak medallion portraits c.1540 at Stirling Castle. His projects included; the fittings of the royal suite on the yacht Unicorn; an engraved brass for the tomb of David Beaton's parents at Markinch in 1541; and a carved lion and a Latin inscription for the tomb of James V in 1542. He made a cradle for Prince James, the short-lived son of James V and Mary of Guise, and a bed for Regent Arran. Andrew made moulds for use in the gun-foundry at Edinburgh Castle, for placing the royal arms and ciphers on cannon barrels, and also engraved ciphers and dates on the guns. He was appointed a gunner in the Scottish artillery on 3 August 1543 with a monthly salary of £3.
Andrew also worked for Edinburgh town with an annual retainer of 10 marks. In 1554 he completed the quire stalls of St Giles Cathedral. The gunner's expertise with ropes lifting cannon was also used by the town council. On 22 February 1555, Andrew and his two Flemish colleagues from the royal artillery met the town's master wrights to discuss how the new timberwork of Tolbooth belfy and steeple would be hauled into position. The following Monday the work began, and in the next week the framework of the belfy, called a "brandrauth" was raised by 28 men "by force at once."
On 28 December 1561, Mary, Queen of Scots made him 'Master Wrycht and Gunnare ordinare' for life. For this, Andrew had a monthly salary of £8-6s-8d. In August 1579, on his death, the position was given to his son Francis.
The Lord High Treasurer's accounts describe Andrew's work engraving the royal cannon in March 1542 in these words;
"Gevin to Andres Mensioun for graving of the Kingis grace armes with unicornis, thrissillis, and flour de lyces upoune the samin piece, and graving of the dait of yere upoune the mouth thairof, and upoun ..., sindry utheris pieces sett in task by Johnne Drummond to him, £13-6s-8d."
Four Scottish falconets with 'IRS' (Iacobus Rex Scotorum) royal ciphers were captured by the English at the battle of Solway Moss, and another was recovered from Castle Semple Loch and is now in the collection of Glasgow Museums.
On the basis of the commission for Cardinal Beaton at Markinch, the historian David McRoberts raised the possibility that Mansioun was responsible for carved oak "Beaton panels" now in the National Museum of Scotland, which carry the Cardinal's heraldry.
Little is known of Andrew's origins, but the Scottish exchequer records consistently describe him as French. As one of the royal gunners, Andrew was hurt defending Edinburgh Castle from the English invasion of 1544 that opened the war of the Rough Wooing. One of his own cannon had backfired, and in June 1544 he was given 44 shillings to pay for treatment to his hand. Later, his salary or pension was increased to compensate him for his hand's lameness.
Andrew stayed in Edinburgh, where he had his own workshop (a buith), and the terms of his pension or retainer of 10 marks in 1554 mention his sons.
Several descendents continued as carpenters (called wrights). Francis, who took his place at Edinburgh Castle in 1579, was probably the eldest son. Francis Mansioun was the official of the trade organisation in Edinburgh as 'Deacon of the Wrights' in 1595, and as such he was asked to comment on the repair of St Giles Cathedral. Joshua and Isaac Mansioun, probably siblings, were also Deacons of the Wrights in Edinburgh.