When William Stanier joined the LMS Railway on the 1st January, 1932, the only modern express locomotives the company possessed were seventy Royal Scot class 4-6-0s, placing the LMSR at a disadvantage against the other Railway Companies. To run non-stop between London and Glasgow, Stanier needed a new 4-6-2 Pacific that could incorporate a wide firebox and large grate needed for the route.
With both three and four cylinder designs being prepared for the new Pacific, Stanier opted for four cylinders, feeling that the balance was better and the hammer blow less. A number of the locomotive's design elements were inspired by the GWR's King class, unsurprising given Stanier's Swindon background as assistant to Charless Collett. The wheels were of the same diameter, the cylinders of the same dimensions and the boiler pressure and tractive effort were identical but many more aspects of the design were to prove very 'Stanier-esque', setting a precedence for future LMS steam locomotives.
The first batch of locomotives to be ordered by the LMSR's Locomotive Committee was to consist of three engines but in February 1933 a recommendation was approved to build the third locomotive as a geared turbine engine. The first locomotive, No. 6200, emerged from Crewe Works on 27 June 1933, unnamed and in works grey which travelled to Euston for the official unveiling. By the time of the official Press trip on 15th August, the locomotive had been named as The Princess Royal and although the first run was aborted due to an uncharacteristic hot axle box failure, enough performance was exhibited to excite the railway press. 6200 The Princess Royal was eventually joined in service by 6201 Princess Elizabeth on the 2nd November and for nearly two years, the two 'Lizzies' worked the West Coast Main Line on a mixture of sevrice trains and high speed tests.
An order for a further ten Princess Royals was placed in June 1934, with them entering service between July and October 1935. These locomotives had a number of improvements over the originals, the most obvious difference being the boilers with shorter barrels and longer fireboxes but different barrel rings, minor frame changes, alterations to the top feed, different chimneys and slidebars, rearranged mechanical lubricators, redesigned reversing gear rods and higher sided tenders which all added to the list of differences. The Princess Royal class served the LMS and British Railways with distinction but in October 1961 the first four locomotives were withdrawn, the final withdrawal taking place in November 1962.