James Watt was born in Greenock, Renfrewshire, Scotland, to Agnes Muirhead and James Watt, a shipwright, ship owner and contractor. He received early education at home from his mother, and later attended Greenock Grammar School. Ill health prevented regular school attendance, but this allowed him to indulge in a self-directed education, demonstrating early aptitude for mathematics, reading, and craftsmanship.

At the age of 18, Watt traveled to London to train as an instrument maker. However, due to his delicate health, he was only able to complete a one-year apprenticeship with John Morgan. This provided him with fundamental skills in crafting precision instruments which became critical in his later career.

Watt returned to Scotland and sought employment as an instrument maker. The Glasgow Guild of Hammermen, citing his lack of a full apprenticeship, initially barred him from opening a shop. The University of Glasgow, however, came to his rescue, offering him a workshop within the university grounds. This position gave him access to academics, equipment, and the intellectual environment that greatly influenced his future inventions.

While working at the University of Glasgow, Watt was tasked with repairing a model of the Newcomen steam engine. He quickly identified its inefficiencies, particularly the wasteful heating and cooling of the cylinder in each cycle. This sparked his intense focus on improving steam engine technology.

Watt conceived the revolutionary idea of a separate condenser to maintain the cylinder at a constant temperature, significantly improving the engine's efficiency. This crucial innovation, patented in 1769, became the cornerstone of the Watt steam engine and set it apart from the Newcomen engine.

Watt obtained a patent for his separate condenser steam engine. Although this invention was a significant step forward, he lacked the capital and manufacturing capabilities to commercialize it effectively at this time. His patent secured his intellectual property, paving the way for future collaborations and commercial success.

Watt formed a partnership with Matthew Boulton, an entrepreneur from Birmingham, England. Boulton provided the business acumen, financial resources, and manufacturing expertise needed to bring Watt's steam engine to market. This partnership, Boulton & Watt, was incredibly successful, and together they developed and manufactured advanced steam engines.

Following the partnership with Boulton, Watt developed the Watt steam engine in 1776, which was fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world. The most important component of the Watt steam engine was his separate condenser which made the engine far more efficient than previous steam engines.

Recognizing the limitations of the original reciprocating (up and down) motion of the steam engine, Watt invented mechanisms to convert it into rotary motion. This opened up vast new applications for the steam engine, allowing it to power machinery in factories, mills, and eventually, transportation systems. He used the sun and planet gear system because he did not want to use the crank system, this was because a rival had previously patented it.

Watt invented the double-acting engine, where steam acted alternately on both sides of the piston. The double-acting engine increased the speed and power of the engine, allowing for even greater efficiency of Watt steam engines.

In the effort to better regulate and understand the working conditions of his steam engines, Watt invented the pressure indicator. This tool allowed engineers to measure steam pressure, enabling them to optimize engine performance and to make safety adjustments. This invention was an early step in the field of control engineering, and allowed for more efficient and safer operation of steam engines.

James Watt died at his home, Heathfield Hall, near Birmingham, England, at the age of 83. He was widely revered for his contributions to the Industrial Revolution and remembered as a brilliant inventor and engineer whose innovations transformed the world. His legacy lives on through the many technologies and industries that his steam engine helped to create.