When the three companies merged in 1844 to form the Midland Railway, Derby became its headquarters and the workshops merged to become the Midland Railway Locomotive Works.
The immediate task was to achieve some standardisation in the various locomotives that it had inherited.
Locomotives at that time were designed and built by manufacturers who might be lacking in actual operating experience with their products.
The first Locomotive and Carriage Superintendent was Matthew Kirtley who persuaded various manufacturers to build to his own design and in 1849 50 six-coupled goods engines were delivered.

After improving the workshops and facilities, including a second roundhouse in 1847, he persuaded the directors that the railway should build its own engines.
New building began in 1851 with passenger engines to the "Jenny Lind" pattern, and more standard goods.
He then produced a large "single" with six-foot six-inch driving wheels.
Throughout its existence the Midland never became fully self-sufficient, usually having its locos built by private contractors to its own designs.
Initially there was some resistance on the part of Sharp Stewart and Stephenson, who quoted over-long delivery times, so that Kirtley had to accept the maker's own designs.
These were good enough, however, that Fowler built some more to a similar pattern.
In 1861 he built four 0-6-0 banking engines for the Lickey Incline with four-foot drivers instead of the usual five feet.
Kirtley's first 2-4-0 was a rebuilt 2-2-2 but he went on to build six for use to King's Cross, then 15 more.

A further, much larger, roundhouse was built in 1852, followed by a large rectangular engine shed with two turntables in 1890.
The original North Midland workshop, which by then had become offices, was raised by one storey in 1859–60, the clock tower being increased in height accordingly.
A long footbridge was added from the entrance door to the front of the station, of which only a fragment remains today.
A third floor was added in 1893.

Another of Kirtley's achievements in 1859 was, at last, to solve the problem of coal burning, by combining the brick arch with a firehole door deflector plate and a blower to increase the draught.
Research into track wear was carried out by Robert Forester Mushet, who produced the first double-headed rail using Bessemer steel.
Whereas wrought iron rails lasted typically six months, a length of steel rail laid near Derby station 1857 was still in use in 1873.

Kirtley also introduced a system of templates and gauges based on the Whitworth system.
Meanwhile, wrought iron axles failures were a problem.
In 1870–1871, Kirtley began a programme of research which eventually resulted in the introduction of steel.

By the end of the 1860s the works had expanded to such an extent, that he was considering reorganising it; and, in 1873, it separated into the Locomotive Works, remaining behind the station, and Derby Carriage & Wagon Works, further south, off Litchurch Lane.
When the three companies merged in 1844 to form the Midland Railway, Derby became its headquarters and the workshops merged to become the Midland Railway Locomotive Works. The immediate task was to achieve some standardisation in the various locomotives that it had inherited. Locomotives at that time were designed and built by manufacturers who might be lacking in actual operating experience with their products. The first Locomotive and Carriage Superintendent was Matthew Kirtley who persuaded various manufacturers to build to his own design and in 1849 50 six-coupled goods engines were delivered.
After improving the workshops and facilities, including a second roundhouse in 1847, he persuaded the directors that the railway should build its own engines. New building began in 1851 with passenger engines to the "Jenny Lind" pattern, and more standard goods. He then produced a large "single" with six-foot six-inch driving wheels. Throughout its existence the Midland never became fully self-sufficient, usually having its locos built by private contractors to its own designs. Initially there was some resistance on the part of Sharp Stewart and Stephenson, who quoted over-long delivery times, so that Kirtley had to accept the maker's own designs. These were good enough, however, that Fowler built some more to a similar pattern. In 1861 he built four 0-6-0 banking engines for the Lickey Incline with four-foot drivers instead of the usual five feet. Kirtley's first 2-4-0 was a rebuilt 2-2-2 but he went on to build six for use to King's Cross, then 15 more.
A further, much larger, roundhouse was built in 1852, followed by a large rectangular engine shed with two turntables in 1890. The original North Midland workshop, which by then had become offices, was raised by one storey in 1859–60, the clock tower being increased in height accordingly. A long footbridge was added from the entrance door to the front of the station, of which only a fragment remains today. A third floor was added in 1893.
Another of Kirtley's achievements in 1859 was, at last, to solve the problem of coal burning, by combining the brick arch with a firehole door deflector plate and a blower to increase the draught. Research into track wear was carried out by Robert Forester Mushet, who produced the first double-headed rail using Bessemer steel. Whereas wrought iron rails lasted typically six months, a length of steel rail laid near Derby station 1857 was still in use in 1873. 
Kirtley also introduced a system of templates and gauges based on the Whitworth system. Meanwhile, wrought iron axles failures were a problem. In 1870–1871, Kirtley began a programme of research which eventually resulted in the introduction of steel.
By the end of the 1860s the works had expanded to such an extent, that he was considering reorganising it; and, in 1873, it separated into the Locomotive Works, remaining behind the station, and Derby Carriage & Wagon Works, further south, off Litchurch Lane.
Derby Works