Thorne was born in Hockley, Birmingham, on 8 October 1857. His father and relatives worked as brickmakers. Thorne's father died in a fight when Thorne was just seven years old. Thorne began working at the age of six, turning a wheel for a rope and twine spinner, working from six in the morning to six at night, with half an hour's break for breakfast and an hour for dinner. Thorne recalls that when the spinner wanted to reduce his wages from 2 shillings and 6 pence to 2 shillings, he "went on strike" and never returned to the job.
The family was on poor relief. Thorne's mother and three sisters worked all hours sewing hooks and eyes. "It was here I had intimate experience with sweated labour", he commented without irony. Thorne took a job with his uncle at a brick and tile works, and later, at another brickworks further away. At the age of nine, Thorne recalled: "my mother got me up at four o'clock every morning to give me my breakfast". It was a four-mile walk to work.
I had to give up this job finally because my mother said that the work was too hard and the distance too long for me to walk every morning and night.
I remember her telling me that the 8 s[hillings] a week would be missed; some one would have to go short. But it was no use being slowly killed by such work as I was doing, and it was making me hump backed. It was not until I had been away from the work for several weeks that I was able to straighten myself out again.
Thorne served for many years on West Ham Town Council and was Mayor from 1917–18.
In 1882, Thorne moved to London and found employment at a gasworks. Thorne joined the Social Democratic Federation (SDF) and became branch secretary. Barely literate, Thorne improved his reading skills with the assistance of Karl Marx's daughter, Eleanor Marx.
In 1889, he helped to found the National Union of Gas Workers and General Labourers, one of the prominent New Unions and became its general secretary. He retained this position in the union and its successors, which became the GMWU in 1924, up to 1934. Thorne also helped to organise the London Dock Strike in 1889.
He contested several elections as a Labour candidate; before finally winning a seat representing West Ham South at the 1906 general election. He remained with SDF as it became the British Socialist Party, but he supported British involvement in World War I. He supported the call for conscription despite the opposition of his local Labour Party branch. As a result, he joined the National Socialist Party.
Thorne visited the Soviet Union shortly after the Russian Revolution of 1917.
He won the seat of Plaistow in 1918 and retained it until his retirement at the 1945 general election, aged 87 — the oldest sitting member at the time. He was appointed Commander of the Order of the British Empire (CBE) in 1930.
A Greater London Council blue plaque, unveiled in 1987, commemorates Thorne at his home, 1 Lawrence Road in West Ham.