Sir Crawford was director of several businesses in Belfast, including Maguire and Patterson, a dry goods firm (Vespa matches), and the Classic Cinema at Castle Place, as well as owning McCullagh and Co., a silk mercers, milliners and fancy drapery store taken over by Styles and Mantles in 1927.
He was elected to Belfast City Council for the Irish Unionist Party. In 1911, he was the High Sheriff of Belfast, and from 1914 to 1917 Lord Mayor of Belfast. McCullagh was knighted in 1915. A Belfast Telegraph report stated that Sir Crawford called for five minutes of silence on 1 July 1916, following news of the slaughter of thousands of soldiers from the 36th (Ulster) Division. Thus, he became the first recorded person to publicly call for a 'silent' tribute for fallen soldiers.
In the Northern Ireland general election, 1921, he was elected for Belfast South for the Ulster Unionist Party. He lost his seat in 1925. From 1931 until 1942, McCullagh was again Lord Mayor of Belfast, which now entitled him to a seat in the Senate of Northern Ireland. He was created a baronet on 1 July 1935.
Letters Patent have passed the Great Seal of the Realm granting the dignity of a Baronet of the United Kingdom to The Right Honorable Sir Crawford McCullagh of Lismara in the parish of Carnmoney in the County of Antrim (1868-April 13, 1948), Ulster Unionist politician, Knight, thrice Lord Mayor of Belfast (1914-17, 1931-42, & 1943-46) and his heirs male of his body lawfully begotten. Whitehall, July, 1935.
He was Deputy Speaker from 1939-41. In 1938 he negotiated with Lord Shaftesbury a donation to the city of Belfast Castle and its demesne of 200 acres bordering on Hazelwood and Bellevue pleasure grounds. In 1941, he was appointed to the Privy Council of Northern Ireland. From 1943 until 1946, he served a third and final term as Lord Mayor.
As the Rt Hon Sir Crawford McCullagh Bt, JP, DL, he lived well at Lismarra, Carnmoney, near Belfast. Lismarra was built by Sir Charles Lanyon in 1850 for John Finlay, who was a flax merchant. The house is made from golden sandstone, and has a grand front entrance with a tall wooden door and several sandstone pillars. From 1895 until 1915 Edward Robinson, of Robinson and Cleaver's department store, lived there. General Dwight Eisenhower was Sir Crawford's most famous visitor at Lismarra in 1945. The house was turned into a nursing home and renamed Abbeydene following his death, and is now an exclusive guest house.