About 1779, Samuel Crompton succeeded in producing a mule-jenny, a machine which spun yarn suitable for use in the manufacture of muslin. It was known as the muslin wheel or the Hall i’ th’ Woodwheel, from the name of the house in which he and his family now lived. The mule-jenny later became known as the spinning mule. There was a strong demand for the yarn which Crompton was making at Hall i’ th’ Wood but he lacked the means to take out a patent. The prying into his methods forced Crompton to choose between destroying his machine or making it public. He adopted the latter alternative after promises by a number of manufacturers to pay him for the use of the mule but all he received was about £60. He then resumed spinning on his own account, but with indifferent success.

On 16 February 1780 at Bolton Parish Church, Crompton married Mary Pimlott (or Pimbley). They had eight children including George Crompton (born 8 January 1781), who followed in the family business.

As the mule was unpatented others soon manufactured it. The machine was constructed in iron, power was applied to assist the inward motion in 1790 and by 1834 it was fully automatic or self-acting. A survey in 1812 showed there were between 4 and 5 million mule spindles in use. Crompton received no royalties for his invention.

In 1800, a sum of £500 was raised for his benefit by subscription, and when in 1809, Edmund Cartwright, the inventor of the power loom, obtained £10,000 from parliament, Crompton was determined to apply for a grant. In 1811, he toured the manufacturing districts of Lancashire and Scotland to collect evidence showing how extensively his mule was being used, and in 1812 parliament awarded him £5000. With the aid of this money, Crompton started a business as a bleacher and then as a cotton merchant and spinner, but without success. In 1824, some friends and members (including Isaac and Benjamin Dobson, Benjamin Hick, John Kennedy and Peter Rothwell) of Bolton’s Black Horse “prosecution” Club, bought him an annuity of £63 without his knowledge.

Crompton died at his house in King Street, Bolton on 26 June 1827, and was buried at the parish church of St Peter’s.