Social justice can be defined as giving all people in society a fair share of equality, dignity, opportunity, education, and material resources. Marx was a materialist, meaning he was chiefly concerned with who received the bulk of society's food, clothing, housing, and education rather than with abstract notions of justice. For him, the working classes could not achieve social justice until they first achieved economic justice: a fair share of society's goods.

Marx looked around at nineteenth-century society under industrialism (a special focus was given to England as the richest, most industrialized, and most powerful nation in the world at the time) and saw grave economic disparities. Working-class people, including young children, toiled for long hours in factories for low wages in dangerous conditions with no job security. Marx found this unjust. "Labor creates all wealth," he declared. Mill owners and other factory owners were becoming vastly wealthy because of their workers' labor, but they paid their workers as little as possible and squeezed as much work as they could out of them. This was wrong, Marx stated, because the workers should benefit from the profits their labor produced. In Capital, he quotes reports of women in factories passing out from exhaustion during sixteen-hour shifts for which they were paid starvation wages.

Many others at the time saw the same injustices wrought by industrialism and wanted to ameliorate them by introducing laws and regulations to protect workers. They fought for eight-hour days, minimum wage, unemployment insurance, safety rules, and other rights we take for granted today. Marx, however, did not believe these measures could work, because experience told him that the capitalist class, by which he meant the very small number of the very wealthy who owned the means of production, would take back any concessions they were forced to make to workers as soon as they could get the upper hand. This was not because they were inherently evil, but because greed was the basis and rationale for capitalism. Capitalists were driven to maximize profits at all costs.

For Karl Marx, therefore, the ideal system of social justice was communism. Under this system, the working classes, which comprised the bulk of the population, would rise up and seize the factories, banks, oil wells ,and other sources of wealth. They would run these entities themselves and equally distribute the profits to achieve the greatest social good. Only through such revolutionary measures, Marx believed, could real and lasting social justice be achieved

For Karl Marx, fundamental concepts of social justice were rooted in economic justice. For Marx, economic inequality, and the existence of private property, resulted in social injustice. One particular concern of his was that when ownership was separated from the means of production, and work from the final product (e.g. a worker who simply uses a machine that makes a small part for a car rather than working on a car as a whole) workers become alienated and unhappy. Thus social justice has two parts. One is "from each according to his abilities and to each according to his needs" -- people doing the work for which they are best suited and all people having their economic needs supplied. The second part is workers owning the means of production and restructuring work so that workers can feel connected to and get emotional satisfaction from their labour.