Schooled privately in Shooter's Hill, he displayed an aptitude for engineering and, from the age of 15, studied for two years at Portsmouth Dockyard before being articled to Messrs. Braithwaite & Milner in London.
In 1846, Parsons was employed on engineering work by John Rennie, engaged as superintendent of large fixed plant and machinery on the Eastern Union Railway.
He then established his own engineering business in London in 1850, being mainly concerned with design and construction of railway fittings, patenting improved switches and axle-boxes.
[1][2] Parson's ordnance inventions included a system of inserting rifled steel tubes into old cast-iron guns, making previously unusable weapons serviceable.
During this time he started studying the use of metals generally, establishing a private mechanical laboratory at his home in Blackheath.