His father had died rector of Rossington, West Riding of Yorkshire, and this preferment was conferred on Jackson by the corporation of Doncaster on his ordination as a deacon in 1708, and as a priest in 1710.

The following year he was presented by Nicholas Lechmere, chancellor of the duchy of Lancaster, to the confratership of Wigston's Hospital, Leicester.

On 22 February 1722, he was inducted to the private prebend of Wherwell, Hampshire, on the presentation of Sir John Fryer; here also no subscription was required.

The mastership of Wigston's Hospital was given to him on Clarke's death (1729) by John Manners, 3rd Duke of Rutland, chancellor of the Duchy of Lancaster.

[2] Jackson married Elizabeth, daughter of John Cowley, a collector of excise at Doncaster, in 1712, and they had twelve children.

Jackson was prompted to take on controversial topics by the publication (1712) of the Scripture Doctrine of the Trinity by Samuel Clarke.

His first publication was a series of three letters, dated 14 July 1714, by 'A Clergyman of the Church of England,' in defence of Clarke's position.

William Whiston, in a letter to William Paul, 30 March 1724, says that Dr. Clarke has long desisted from putting his name to anything against the church, but privately assists Mr. Jackson; yet does he hinder his speaking his mind so freely, as he would otherwise be disposed to do.Almost simultaneously with his first defence of Clarke, Jackson advocated Benjamin Hoadly's views on church government in his Grounds of Civil and Ecclesiastical Government, 1714; 2nd edit.