He worked at the school for adults on Sundays for no pay, despite only going to school himself until he was fifteen. Together with his brother Richard he took over the family business in 1861. In 1878 they acquired 14 acres (57,000 m²) of land in open country, four miles (6 km) south of Birmingham, where they opened a new factory in 1879. He rented ‘Woodbrooke’ – a Georgian style mansion built by Josiah Mason, which he eventually bought in 1881.

George Cadbury married twice. In 1872 he married Mary Tylor, daughter of Quaker author Charles Tylor: she died in 1887. She was the mother of George Jr, Mary Isabel, Edward, Henry, and Eleanor Cadbury.

In 1888 he married Elizabeth Mary Taylor. They had six children together: Laurence John, George Norman, Elsie Dorothea, Egbert, Marion Janet, and Ursula.

In 1901, disgusted by the imperialistic policy of the Balfour government and opposed to the Boer War, Cadbury bought the Daily News and used the paper to campaign for old age pensions and against the war and sweatshop labour.

George Cadbury was one of the prime movers in setting up The Birmingham Civic Society in 1918. Cadbury donated the Lickey Hills Country Park to the people of Birmingham. He also donated a large house in Northfield to the Birmingham Cripples Union that was used as a hospital from 1909. It is now called the Royal Orthopaedic Hospital. In 1890 he, along with a number of other leading Quakers, helped re-establish Grove House School as Leighton Park School in Reading as the leading Quaker school in Britain.

He died at his home, Northfield Manor House, on 24 October 1922, aged 83.

The George Cadbury Carillon School was opened in 2006 and is the only carillon school in the United Kingdom.