He was educated at the University of Edinburgh, where he graduated M.A., "with no small applause," whilst in his fifteenth year (7 April 1675), writing his surname Sheils.

Strict measures being taken shortly after (1684) for the enforcement of the oath, Shields proclaimed its sinfulness, and his licensers threatened to withdraw their licence.

On Sunday, 11 January 1685, he was apprehended, with seven others, while preaching from the words in Genesis xlix., 21 : "Naphtali is a hind let loose," — afterwards the title of his famous Treatise.

[4] Captured by the city marshal at this conventicle in Embroiderers' Hall, Gutter Lane, Cheapside, he was brought before the lord mayor, who took bail for his appearance at the London Guildhall on the 14th.

[7][8] Anderson says: "About the autumn of 1686, he with the other ministers imprisoned in the Bass were brought to Edinburgh, and had their liberty offered them, provided they would engage to live orderly.

Refusing when brought before the Council, to come under this engagement, he was recommitted to the tolbooth of Edinburgh, but he succeeded in making his escape from it disguised in women's clothes."

"[9] Shields made his way at once to Renwick, whom he found on 6 December 1686 at a field conventicle at Earlston Wood, parish of Borgue, Kirkcudbrightshire.

[10] On 22 December, at a general meeting of Renwick's followers, he publicly confessed the guilt of "owning the so-called authority" of James VII of Scotland.

[12] After Renwick's execution (17 February 1688) Shields pursued his policy of field meetings, preaching on a celebrated occasion at Distincthorn Hill, parish of Galston, Ayrshire.

[13] He certainly approved of the Cameronian insurrection, under Daniel Ker of Kersland, at the end of the year, when the incumbents of churches in the west were forcibly driven from their charges.

On 3 March 1689, with Thomas Lining and William Boyd, he took part in a solemn renewing of the covenants by a concourse of people at Borland Hill, parish of Lesmahagow, Lanarkshire.

[11] After the Revolution Shields joined the Church of Scotland, and was received into communion, 25 October 1690, with his associates, Thomas Lining and William Boyd.

[4] On 21 July 1699 he was authorised by the commission of the general assembly to proceed, with three other ministers, Francis Borland, Alexander Dalgleish and Archibald Stobo, and a number of colonists, to Darien, this being the second expedition in pursuance of the ill-fated scheme of William Paterson.

Shields and his companions were really the first foreign missionaries of the Church of Scotland, the Commission of Assembly having, on 21 July, charged them "particularly that you labour among the natives for their instruction and conversion, as you have access.

In a letter to the Presbytery of St Andrews, dated 2 February 1700, Shields wrote :"Our meetings amongst ourselves are in the woods, where the chattering of parrots, mourning of pelicans, and din of monkeys is more pleasant than the hellish language of our countrymen in their huts and tents of Kedar; and our converse with the Indians, though with dumb signs, is more satisfying than with the most part of our own people.

"[14] Shields made some expeditions inland; at length, with Francis Borland, he crossed over to Jamaica, but had scarcely arrived there before he went down with fever.

[11] On the failure of the Expedition, he sailed for Scotland, heart-broken by the profligacy of the settlers and the little success his labours had met among them, but died of malignant fever in the house of Isobel Murray, Port Royal, Jamaica, 14 June 1700.

Shields was "of low stature, ruddy complexion, quick and piercing wit, full of zeal, and firm in the cause he espoused; pretty well skilled in most branches of learning, in arguing very ready, only somewhat fiery; but in writing on controversy he exceeded most men of that age.