Bannerman started playing rugby union while at school, and between 1919–20, he was captain of Glasgow High School's 1st XV. Bannerman was an accomplished sportsman winning a "rugby blue" at Oxford
He won 37 caps for Scotland between 1921 and 1929 and was Scotland’s most capped player until 1962 when Hugh McLeod surpassed his total. He played in Scotland’s first “grand slam” winning team in 1925, securing this achievement by beating England in the opening match of the new Murrayfield Stadium.. He went on to become Glasgow HSFP's most capped player.
Bannerman became active in Liberal politics from the 1930s. He was particularly interested in the problems of depopulation and unemployment for ordinary people in the Scottish Highlands and islands. From 1942 to 1957 he was a Forestry Commissioner. In 1938 he was adopted as prospective Liberal parliamentary candidate for Argyll. When the seat fell vacant in 1940 it was mooted that Bannerman might run as a Liberal National but the negotiations with the Conservatives broke down robbing him of his best chance of entering the House of Commons. He contested Argyll unsuccessfully in the 1945 general election and Inverness in 1950. But in 1954 he was the candidate in an extraordinary by-election at Inverness which some historians have seen as a true turning point in Liberal fortunes in Scotland and perhaps the United Kingdom. From a position where there had been no Liberal candidate in the 1951 election, Bannerman jumped into second place over Labour, coming just 1331 votes behind the Tory winner. This was the best Liberal by-election performance since the war. At the general election of 1955, Bannerman came even closer, losing by just 966 votes. Although his vote share declined in the 1959 general election, the ground had been laid for a successful attack on the seat in the 1964 general election by Russell Johnston, who held the seat until he retired from the Commons in 1997. Bannerman was chairman of the Scottish Liberal Party from 1954 to 1964 and Rector of Aberdeen University in 1957. He made other attempts to enter the Commons, including giving Labour a close run at the Paisleyby-election of 1961, registering 41.3% of the vote in a seat where there had been no Liberal candidate at the 1959 general election. He tried again without success at Paisley at the 1964 general election but in December 1967 he was made Baron Bannerman of Kildonan, of Kildonan in the County of Sutherland, and so finally entered Parliament.
Life peerage
Bannerman was one of three Liberals to be made life peers in 1967; the others were Tim Beaumont and John Foot. Their appointments were attacked by the Young Liberals as undemocratic. One particular critic was Tony Greaves, then editor of the Young Liberal publication Gunfire, who argued that as the Liberal Party was in favour of a new social and political order, it was quite wrong to participate in the most pathetic feature of the existing order, the House of Lords.. In his maiden speech in the Lords, Bannerman took up the Scottish cause, referring to the anger of Hamilton where the Scottish National Party had just won a parliamentary by-election; and warning it was the anger of two centuries in which the Scots had been a "sleeping partner" in the United Kingdom political scene.
Gaelic culture
In 1922 he won the prestigious gold medal for solo singing at the Royal National Mòd in Fort William. He was President of An Comunn Gàidhealach, the national Gaelic Society, a position previously held by his father, from 1949 to 1954.
