As a young man, he working in the quarries of the Isle of Purbeck: he was reputedly one of the last people to work in the quarry at Tilly Whim and, as a stonemason, on the Isle of Wight. He travelled to London in 1807 where he started working for Henry Westmacott, the Government mason and builder, as a general foreman: Mowlem personally worked on Nelson"s Tomb in Street Paul"s Cathedral, Somerset House and the Royal Mews at Charing Cross. In 1822 he set up business as a paving contractor and stone merchant, building up a large business and paving Blackfriars Bridge amongst other areas.
In 1839 Mowlem moved briefly to Guernsey, which was the source of much of the granite used by his business.
He died in 1868, childless, and the business, which ultimately became known simply as Mowlem passed on to Burt.