At the general election of 1754 Mackenzie made an unsuccessful bid for Ross-shire, but was returned on the joint Argyll-Bute interest for Ayr Burghs. Listed by Dupplin as attached to Argyll, in Parliament he rarely spoke. On Bute’s junction with Pitt he went into opposition against the Newcastle-Fox Administration over the subsidy treaties and voted, 13 Nov. 1755, against the Address.
Mackenzie tackled his new duties with vigour, competence, tact, and almost unfailing good humour, employing William Mure as his principal deputy. ‘A man of strict honour’, he disliked jobbery, and, though always ready to help his friends to preferment, was scrupulous in insisting that the best qualified man be appointed, whatever his ‘name or surname’ might be, and only rarely gave way to political pressure.
When Bute resigned, he secured for his brother the office of lord privy seal [S], worth £3,000 p.a., and his continuation as Scottish minister. The King indeed insisted with Grenville that in Scottish affairs he must take ‘all recommendations from Mr. Mackenzie’.
I find ... not only in Lord Garlies but in every Scotch nobleman or gentleman I speak with, a repugnance to have anything to do with Mr. Mackenzie, who has not the good fortune to be much liked by his countrymen.
Although ‘tired to death with attendance on the House’ during the late sittings on Wilkes and general warrants, Mackenzie scrupulously dealt with every aspect of Scottish business, from University affairs, banking, the annexed estates, fisheries and manufactures, and even initiated conferences on the preparation of a reform bill ‘to put a stop to that abominable practice of splitting votes for the purpose of elections’, almost invariably consulting Bute on his line of conduct.
The lord and lady privy seal take extremely upon them when they are in Scotland. I never have a letter from her that does not say what a vast deal of business both public and private he has. For the public I can’t pretend to judge. For the private ... I do remember ... at Dalkeith ten years ago ... he used to tire me to death with the same bags of dirty papers he brought out and looked over, and by all I could find out, it was only to settle how many men would be sufficient to weed some quickset hedges ... at a place of his in Angus ... Betty was really a very good kind of woman till she became sister [-in-law] to a minister and wife to a man that thinks himself one.
When in April 1764 Mackenzie conscientiously declined, on point of merit, to nominate to the Scottish bench a brother-in-law of Sir Lawrence Dundas, Grenville’s friend, the King wrote to Bute:
I am glad there has been this struggle of the ministers, for I will show them who recommends Scotch offices. I have ever declared Mr. Mackenzie for that department; I will settle that matter instantly and if they have not understood my orders on this occasion it is not for want of explaining the thing clearly. My words were that Mr. Grenville should see Mr. Mackenzie and desire him to name the person whose character would best supply the vacant gown ... as I understand my d. friend had settled with Mackenzie the judge I will hasten the execution of it.
When in May further vacancies occurred, Mackenzie, after consulting Bute, diplomatically agreed to recommend Dundas’s relation ‘though perhaps not the properest person’.
Mr. Grenville has come a great deal out of his way to attack me with such violence, and if the King pleases that Grenville should intermeddle in that manner with the affairs of this part of the kingdom all I would beg is that I may be allowed to retire from them; for ’tis impossible for me to go through all the variety of plagues that I have and at the same time be liable to the mortification of being thwarted and controlled and teased to death by such a man as he is.
When further inquiry proved that Fife had no real grounds for his accusations, Grenville was obliged to climb down, but friction continued. Jenkinson’s attempts at reconciliation bore some fruit when a few months later the question of a new application for the sheriffship of Banff arose, and Mackenzie yielded to Grenville’s insistence upon the appointment of Fife’s nominee, whom he personally considered ill-qualified. He wrote to Mure, 27 Nov. 1764:
During the abortive negotiations for a new Administration in May 1765, Bute’s ‘banishment’ and Mackenzie’s status were vital issues, and when the King was obliged to invite the Grenville ministry to continue, they made it a principal condition that Mackenzie should be removed both from the managament of Scotland and his office of privy seal.
His Majesty answered: ‘that as to the first it would be no great punishment ... to me, as I had never been very fond of that employment; but that as to the second I had his promise to continue in it for life ... If you force me ... to violate my royal word, remember you are responsible for it, not I.’
When Grenville offered to ‘make some arrangement for Mr. Mackenzie’ the King scathingly replied: ‘If I know anything of him, he will give himself very little trouble about your arrangements for him.’ Rather than ‘throw the country into confusion without a government’, the King, on receipt of a letter from Bute releasing him, in his own and Mackenzie’s name, ‘from the promise, was obliged to yield.
When a few weeks later, new negotiations began for a change of ministry, the King made Mackenzie’s reinstatement a major issue. Pitt, when approached, proposed for Mackenzie ‘some other office equivalent in value to that he had quitted but without power’.
On the formation of the Rockingham Administration, Mackenzie wrote to Mure, 11 July 1765:
As to myself, I shall remain as I am, out of office ... My brother (after a conversation he and I had together) wrote a letter to the King, begging that his Majesty would allow me to decline all office, rather than obstruct any arrangement of Government which might be thought expedient for his service. This being the state of the case, I am mighty well pleased in being as I am.
Some ten days later he went to Scotland and en route visited Lord Northumberland, with whom he discussed plans ‘for the King’s friends connecting themselves together closely and acting in a body’. He wrote to Jenkinson, 4 Aug.:
[Pitt] then attacked the pusillanimity of the present ministry for not having dared replace him, not indeed as a minister for Scotland, but to enjoy an office he every way deserves, and to which his sovereign’s goodness had raised him.
All parties now sought the support of Bute’s friends. On Grafton’s resignation the Cabinet were prepared to make concessions; Conway proposed that Mackenzie should have the ‘first proper employment’ vacant, and suggested the vice-treasurership of Ireland.
On the formation of the Chatham Administration, Mackenzie was at once reinstated in his office of privy seal without prior consultation with Bute. ‘My being restored ... was solely and entirely the King’s own act’, he wrote to Mure, 3 Sept.
On Grafton’s resignation, he was one of the parliamentary leaders sent for by North on 29 Jan. 1770,
In the Parliament of 1774-80 Mackenzie, although still solicited by place hunters, more often than not decided not ‘to meddle’ except on behalf of close friends. He went to Italy in the winter of 1777-8; during his absence, so low had his influence fallen that North twice offered the reversion of his office of privy seal to Alexander Wedderburn, who from loyalty to the Bute family declined.
Described by Lady Louisa Stuart as ‘the best humoured mortal alive’,
