After graduating from the University of St Andrews in 1613, he became a teacher of Philosophy there until, in 1619, he entered the ministry and took charge of parish of Keith.
In the following year, on 21 December 1625, he was appointed as the first Professor of Divinity at Marischal College, a post he would hold simultaneously with his charge at Greyfriars.
In 1627, he earned his Doctorate in Divinity, the thesis for which began a long theological dispute with George Turnbull, a Scottish Jesuit theologian.
Baron was a firm supporter of the Anglicanising religious policies of Kings James VI and Charles I.
He opposed the National Covenant of 1638 both through preaching and writings, including three tracts that were co-authored with John Forbes, both of whom, along with four others, were referred to by the Presbyterians as "the Aberdeen doctors".