Born in Glasgow, Scotland, he emigrated to British North America in 1830, settling first in Montreal, then York (now Toronto), and then Hamilton.

At the height of his business career, he had an extensive house and estate in Hamilton, which he named "Auchmar", in recognition of his Clan Buchanan roots in Scotland.

He became prominent in the city's mercantile community, becoming a member of the Merchants House (an organization of businessmen)[1] and an elder at St. David's Church.

He attended the Glasgow Grammar School but his ambitions for a professional career were thwarted by family financial reverses and the death of his father in 1825.

[2][3] At the urging of his elder brother, Peter Buchanan (1805-1860), Isaac located employment as a clerk with the Glasgow firm of William Guild & Company, traders to the West Indies and Honduras.

[2] Buchanan was a commissioned officer in the local militia during the Upper Canada Rebellion, leading troops in Toronto and then on the Niagara frontier.

He complained about the quality of the troops under his command, mainly of Irish background, but he also stated “if I do get to close Quarters with these infernal Rebels and Yankees I am prepared to sell my Life as dearly as I can.”[2] Years later, in 1862 when he was established in the Hamilton area, Buchanan founded the 13th Battalion Volunteer Militia (Infantry), which is one of the predecessors of the Royal Hamilton Light Infantry (Wentworth Regiment).

[2] Buchanan began to demonstrate his political allegiance as a moderate Reformer shortly after arriving in York and taking up business.

He considered them provincial in nature, and resented the strong control which the Anglicans had over the town and the province, compared to his own Scots Presbyterian Church.

In 1835 he issued an extra edition of a local newspaper, stridently calling for equal distribution of the revenue from the Clergy Reserves.

Sydenham was trying to build a coalition which favoured commercial development and excluded from government both the Compact Tories and the "ultra" Reformers led by Robert Baldwin.

[2] Buchanan was nominated for the Toronto riding in the 1841 general election, along with John Henry Dunn, another moderate Reformer, as candidates for the first Legislative Assembly of the new Province of Canada.

The Tories continued to make common cause with the Orange Order in Canada to defend the "British connexion", which they considered endangered by the Reform movement.

The worst of the violence occurred in a riot outside Allan's Tavern, a stronghold of the Orange Lodge, where shots were fired into the crowd from an upper window.

[2][6][7] Charles Dickens, touring North America the next year, recounted the episode: It is a matter of deep regret that political differences should have run high in this place, and led to most discreditable and disgraceful results.

It is not long since guns were discharged from a window in this town at the successful candidates in an election, and the coachman of one of them was actually shot in the body, though not dangerously wounded.

[9][10] In the first session of the Legislative Assembly in 1841, Buchanan voted in favour of the union of the Canadas, and was a general supporter of Lord Sydenham's policies.

[13] On the key issue of responsible government, Buchanan disagreed with the position taken by Baldwin, who considered that the Governor had to appoint an Executive Council which had the support of a majority of the Legislative Assembly.

While in office, he attempted to promote his railway interests but also negotiated refinancing of the city of Hamilton's debts after it borrowed heavily to finance infrastructure improvements.

The grounds included a manor house named "Auchmar", after the Buchanan estate his father had purchased before his financial troubles.

One of the couple's sons, James Isaac Buchanan, worked as a banker in Pittsburgh, Pennsylvania and made a substantial fortune.

Some of his writings include: The Isaac Buchanan and Family fonds is an extensive collection held by Library and Archives Canada.