Foulis was elected commissioner for Edinburghshire on 20 January 1685, was a supporter of the extreme measures of the government, but continued to sit after The Glorious Revolution, 'until his seat was declared vacant, 25 April 1693, because he had not taken the oath of allegiance and signed the assurance'.
This money was used to fund the ill-fortuned Darien Scheme to establish a Scottish trading colony on the isthmus of Panama.
[4] After the death of William III & II Foulis was made colonel of the Midlothian militia, and sworn of the privy council (1703).
[5] Although publicly he spoke in opposition to the Union of 1707, under the terms of the Act, he, and the fellow stockholders of the Company of Scotland were all fully "compensated" for their losses.
[4][7] Colinton Castle remained in the hands of the Foulis family until 1800 when it was bought by William Forbes of Pitsligo as his Edinburgh residence.
Foulis was engaged in a complex lawsuit with Dame Margaret Erskine, Lady Castlehaven, his stepmother, as to her interest in his father's estates.
The chief papers were published, with notes by him, or compiled under his direction, and exhibit some details as to Scotch aristocratic life and customs of the period ('An Exact and Faithful relation of the Process pursued by Dame Margaret Areskine, Lady Castlehaven, against Sir James Foulis, now of Collingtoun,' Edinburgh, 1690).