He then entered the Royal Navy, and continued in the Naval Service for five years, when, directing his attention to the study of law, he was called to the Bar of Scotland in 1820.

Subsequently, in 1840, on a vacancy occurring in the metropolitan sheriffdom, he was offered and accepted the office of sheriff of Edinburgh, which he held until his death.

A renewed application to Parliament was made in the spring of 1847, and a select Committee was then appointed to inquire in what parts of Scotland, and under what circumstances, sites had been refused.

[3] It was reported to the House of Commons, was that the Committee held it to be proved that there were a number of Christian congregations in Scotland who have no place of worship within a reasonable distance of their home, where they can unite in the public service of Almighty God, according to their conscientious convictions of religious duty, under convenient shelter from the severity of a northern climate.

And the Committee farther reported to the House that they had heard with pleasure, in course of the evidence, that concessions had been made and sites granted; and they expressed an earnest hope that those which have hitherto been refused may no longer be withheld.

[3] At the Assembly in 1846 Speirs gave voice to the fear that proprietors were “sending away or ejecting the Free Church population, in order that they may in that way take away the pretext for asking sites”.

Addressing the Commission of the Free Assembly in November 1845, he revealed that he had placed a contract with Mr John Wood of Port Glasgow for an iron church capable of containing 700 sitters.

At the cost of slight inconvenience to the congregation, a mooring was chosen below the township of Ardnastang, in the bay of Eilean a’Mhuirich, about 1.25 miles west of Strontian.

In connection, with Prison reformation and discipline, he was an active member of the society formed in 1835 on that subject, which by its efforts materially contributed to the enactment of 1839, by which the jails of Scotland, once described as "nurseries of vice and crime," became placed in a more satisfactory condition.

This was reinforced by the social connections he made to other gentry families from his schooldays, through his naval service, when called to the bar and through marriage.

In parallel with that policy Speirs had acted decisively to win the propaganda battle, through the construction of an iron floating church and by the lithographs he commissioned of scenes of site-refusal.