He began his career as an apprentice in Colonel James Fletcher's forge in South Northbridge.

Whitin and four of his sons and their descendants would become very influential in the development of the textile industry in the Blackstone Valley area during the 19th Century, establishing or acquiring several mills throughout the Blackstone Valley area, including ones at Uxbridge, Linwood, Riverdale and Rockdale.

Also in 1826, a new brick mill was constructed, having 2000 spindles, which still stands today at Whitinsville, having been recently restored.

Colonel Fletcher's 1772 Blacksmith Forge is also still standing, next to the Brick Mill, on the west bank of the Mumford River.

The Whitinsville Cotton Mill would later be used as a testing facility for new equipment developed by the Whitin Machine Works, across the street.

This was to be first of other successive inventions that would establish the Whitin Machine Works as a great textile machinery company.

In 1847, the Whitins built "The Shop," which consisted of a new textile production area that was four times larger than the brick mill.

During this time also, Paul Whitin Jr. had married Sarah Chapin and built a new Italian-styled home, along with his brother in 1856.

The huge plant is now occupied by a variety of smaller businesses along both sides of the Mumford River in Whitinsville.