Thomas Parker started his professional life as an apprentice under Robert Sinclair at the Greenock Works of the Caledonian Railway. In 1858, he moved to the Manchester Sheffield & Lincolnshire Railway (MS&LR) to become their Carriage and Wagon Superintendent. In this position, Parker produced one of the first dining car designs used in Britain, and a series of 6-wheeled bogie coaches. In 1886, he became the MS&LR's Locomotive Superintendent.
Parker introduced a series of designs with inside frames. Parker was also the first to use Belpaire fireboxes on locomotives intended for British running (Beyer, Peacock & Co had used them previously on locomotives exported to Belgium). Both the Belpaire firebox and the inside frame designs would be continued through to the end of the MS&LR (later GCR) with Grouping in 1923.
Parker also oversaw the complete remodelling of the MS&LR's Gorton Works, and added a new erecting shop to the complex.
Parker retired in 1893, but continued to live near the Gorton Works. He died at Gorton in 1903.