Garratt was born in Hackney and began his working life with the North London Railway (NLR). He became an apprentice, aged 15, at the NLR’s Bow locomotive works. He finished his apprenticeship in 1882 and took a job at Doxford’s Marine Engine works in Sunderland where he worked as an engineer on steamships.

In 1885, Garratt returned to work on the railways. He became an inspector of engines and railway materials for C. Douglas Fox and Alexander Rendel before taking a job with the Vacuum Brake Company inspecting engines for the London & South Western Railway.

In 1889, Garratt travelled abroad to work as an engineer on railways in South America. He was a district locomotive superintendent for the Central Argentine Railway and a locomotive superintendent for the Central Cuban Railway, the Lagos Government Railway and the Lima Railway of Peru.

Garratt returned to Britain in 1906. Early in 1907, he started to work on an idea for a new type of articulated steam locomotive. While working in South America, Garratt observed the operation of articulated engines such as the Fairlie locomotives supplied by the Vulcan Foundry Co. He noticed that these engines had difficulty in achieving good stability, traction and speed on the narrow-gauge track. Garratt designed his cradle-type locomotive with a boiler mounted centrally between a pair of driving bogies. The bogies carried the fuel and water tanks. The articulated design allowed the locomotive to negotiate very tight bends. Garratt showed his design to Kitson & Co., locomotive engineers in Leeds. The company had already developed the Kitson-Meyer articulated locomotive and rejected his proposals.

Around this time Garratt was working as a locomotive inspector for the New South Wales Government. His job was to inspect the locomotives built by Beyer, Peacock for the New South Wales Government Railway. While at Beyer, Peacock’s Gorton works, Garratt took the chance to discuss his patented cradle-type locomotive with the company directors. The company recognised the superiority of Garratt’s design and agreed to work with him on the design.

In March 1907, work began on a proposed articulated compound tank engine for the Tasmanian Government Railway. The Beyer, Peacock & Co. draughtsman, Samuel Jackson, made two general arrangement drawings in April 1907.

Garratt took out a provisional patent on his design in July 1907. One of the Beyer, Peacock & Co. draughtsmen drew up a general arrangement drawing for inclusion with the patent application. This drawing was probably based on the preliminary drawings for the Tasmanian Garratt made in April 1907.

Both Beyer, Peacock & Co. and Herbert Garratt began to look for markets for the Garratt following the granting of the patent in 1907. Beyer, Peacock’s draughtsmen drew up several drawings for proposed Garratt engines, including one for the New South Wales Government in October 1907.

In November 1907, Garratt moved with his family to Levenshulme to be closer to the Beyer, Peacock & Co. works in Gorton. He made a series of oil paintings showing the K1 in steam. He used one of these images for his letter-headed paper and in other promotional literature for the locomotive.

Beyer, Peacock & Co. signed a formal agreement with Garratt to become the sole agent to market, manufacture and sell Garratt locomotives in the United Kingdom. Garratt made similar agreements with companies in other countries, including the Baldwin Locomotive Works of Philadelphia, USA, the Société St-Léonard in Belgium and Henschel & Sohn in Germany. As a result of these agreements, many other Garratt locomotives were built on the principles set out by Herbert Garratt.

Garratt received his full patent for his locomotive design in June 1909. He continued to work with Beyer, Peacock & Co. in Manchester until 1911. He returned to London with his family and died at home in Richmond in September 1913.