Lawson eagerly began work in the colliery the day after he turned twelve. He started as a trapper, opening and shutting doors for the drivers, working a ten-hour day. He was paid ten pence per day, and his life greatly improved - he was treated as an adult now. After a few months he became a driver, with his own pony. After a couple more years, he began off-hand work, braking inclines and attending to the signalling bells. He began attending union meetings, including the annual Durham Miners' Gala, where in later years he met the likes of Will Crooks, Ellen Wilkinson, Ernest Bevin and George Lansbury. At eighteen he became a putter and began speaking and working for the union. With five members of the family now working at the colliery, the Lawsons had a higher status and moved into a house closer to the pit, with a front room. Throughout this period his he gambled frequently and read a lot: Eventually, reading won over gambling. He had read nothing of economics or politics yet, but had developed a strong sense of injustice, firmly believing that manual workers were under-paid and under-valued. These ideas generally seemed strange to his colleagues and family and he kept them to himself. He joined the Methodist Society, and found his ideas more accepted there. Through reading the Labour Leader and the Clarion, Lawson realised he was a socialist. At the age of 21 he met a servant-girl from Sunderland who was staying with friends at Boldon. They were married in February 1905.
In 1905, after his marriage, Lawson became an active speaker for the ILP, expounding socialism and the Labour Representation Committee to the miners of Durham, who had traditionally supported the Liberal Party. Later that year, Lawson joined a correspondence class with Ruskin College, Oxford. The following spring, Lawson received a letter from the college offering him six months' scholarship if he could find the money to pay for the other six months. This was a significant expense that would be compounded by living costs, and as Lawson was determined that he would only ever work as a miner there was no obvious advantage to university study. Canon Moore Ede, a county councillor and later Dean of Worcester, convinced him to go and helped raise some of the fees; Lawson and his wife sold their furniture and saved what they could, and the rest was paid by his parents. His wife moved to Oxford with him, finding work and accommodation as a servant in a series of homes. Amongst his tutors, Hastings Lees-Smith, the vice-principal of Ruskin and a lecturer on economics, had a particular influence on Lawson.
At the end of the year, Lawson was offered a further six months scholarship on the same terms, and after working at Boldon over the winter to raise the money he began his second year of study in February 1908. Halfway through that year, he was told that the College Council had decided to extend his scholarship to cover the rest of the full year. It was suggested he should enter Manchester College, Oxford, to study for a degree. He was grateful but refused, not wanting a professional career; three months later, he returned to Boldon. He became well-known around the county, as a speaker for both the ILP and the union. He was a negotiator for his union lodge and a delegate to the Miner's Council at Durham.
In 1909, he was invited by the union to run for Durham County Council, but he was not yet on the electoral register and was ineligible to stand. Pete Curran, Labour MP for Jarrow, had made Lawson his election agent: this was unpaid, hard work, and consumed all of Lawson's spare time during campaigns, as he travelled to and around Jarrow division. Curran was hit by ill health in the January 1910 general election and had trouble campaigning. He lost by less than 100 votes and died within a week. The Lawson's first daughter, Irene, was born later that year. Whilst campaigning in the general election in December, Lawson was asked by friends in Chester-le-Street to stand for the position of check-weighman at Alma Colliery. Elected and paid by hewers, as a check-weighman he would be responsible for ensuring miners received the full amount due for the coal they dug and would act as their legal representative. Lawson was reluctant to leave manual work, but allowed his name to go forward. Labour lost Jarrow again; at the same time, the miners at Alma, elected him almost unanimously.
Following the end of the war, Jack Lawson was granted temporary leave to contest the Seaham division of Durham in the 1918 general election; he campaigned against war reparations and won only a third of the votes against a coalition candidate. After that he was sent to Clipstone in Derbyshire, where he was demobbed. Returning to work at Alma Colliery and as a county councillor, he started to have health problems and was sick during the council elections the following year. The Labour Party, which entered the election with around a dozen out of one hundred councillors, won control of the council.
Later in 1919, John Taylor, Labour MP for Chester-le-Street since 1906 and a friend of Lawson's, resigned his seat due to ill health. Though reluctant to risk leaving Durham and the colliery for London and Parliament, Lawson was persuaded to stand for Labour in the bye-election. He was sponsored by the Durham Miner's Association and won with a majority of eleven thousand, entering the House of Commons in November 1919.
Ramsay MacDonald appointed Lawson as Financial Secretary to the War Office in the 1924 Labour government. He worked alongside Clement Attlee, and the two came to enjoy a very firm friendship and mutual admiration. Both felt odd, controlling generals they'd served under a few years before, but the generals liked them, considering them less idle than their predecessors. He served as Parliamentary Secretary to the Ministry of Labour in the 1929 Labour government, but refused MacDonald's invitation to join the National Government following the split in 1931.
The 1931 general election was disastrous for Labour, and Lawson was one of only two Durham Labour MPs to keep their seats, out of seventeen who won there in the 1929 election. During the 1930s, Lawson supplemented his income as an MP by writing. He published his autobiography, A Man's Life, in 1932, intended as a record of the family life of miners. He followed this with a novel about miners, Under the Wheels, and biographies of Peter Lee and Herbert Smith. He also wrote for newspapers and periodicals.
With Labour's victory in the general election of July 1945, Lawson was appointed Secretary of State for War, with a seat in Attlee's Cabinet. During the closing months of the war, he travelled thousands of miles, visiting troops in the Far East, and speaking at military functions and mass meetings. His refusal to stick to the scheduled, whitewashed routes on official visits, insistence on seeing everything for himself, and willingness to stop and listen to everyone he met, made him unpopular with senior officers. However, he was very popular with soldiers, who were glad that one of their own was now in the War Office. Lawson over-saw planning for post-war operations, including the occupation of Germany, and for the mass demobilisation, ensuring it happened quickly and smoothly. He also served as one of Attlee's key allies in the Cabinet, particularly during early conflicts with Herbert Morrison. However, from the summer of 1946, Lawson found his job increasingly difficult: he suffered severe health problems and had to go into hospital, retiring from the front bench in October.
In 1949, on Attlee's recommendation, the King appointed Jack Lawson as Lord Lieutenant of Durham. He did not stand for re-election in the 1950 general election, and was created Baron Lawson in March of that year. Lord-Lieutenants are unpaid and Lawson, one of the first working-class men to hold such a position, received income support. He did attend the House of Lords but did not take a front-bench position. Still a close friend of Attlee's, he provided moral support during struggle to hold the Labour Party together during the 1950s. His protégé, Sam Watson, became General Secretary of the Durham Miners and one of the most influential trade unionists in the party; a member of the National Executive Committee for over twenty years, Watson was Chairman of the Labour Party 1949-50. Lord Lawson retired as Lord Lieutenant in 1958 and died in 1965, at the age of eighty-three.