The headquarters were at Euston railway station. As traffic increased it was greatly expanded with the opening in 1849 of the Great Hall, designed by Philip Charles Hardwick in classical style. It was 126 ft (38 m) long, 61 ft (19 m) wide and 64 ft (20 m) high and cost £150,000 (equivalent to £15,280,000 in 2018). The station stood on Drummond Street. Further expansion resulted in two additional platforms in the 1870s, and four more in the 1890s, bringing the total to 15.
The LNWR described itself as the Premier Line. This was justified as it included the pioneering Liverpool & Manchester Railway of 1830, and the original LNWR main line linking London, Birmingham and Lancashire had been the first big railway in Britain, opened throughout in 1838. As the largest joint stock company in the United Kingdom, it collected a greater revenue than any other railway company of its era.
On 1 February 1859 the company launched the limited mail service, which was only allowed to take three passenger coaches, one each for Glasgow, Edinburgh and Perth. The Postmaster General was always willing to allow a fourth coach provided the increased weight did not cause time to be lost in running. The train was timed to leave Euston at 20.30 and operated until the institution of a dedicated post train, wholly of Post Office vehicles, in 1885. On 1 October 1873 the first sleeping carriage ran between Euston and Glasgow, attached to the limited mail. It ran three nights a week in each direction. On 1 February 1874 a second carriage was provided and the service ran every night.
In 1860 the company pioneered the use of the water trough designed by John Ramsbottom. It was introduced on a section of level track at Mochdre, between Llandudno Junction and Colwyn Bay.
The company inherited a number of manufacturing facilities from the companies with which it merged, but these were consolidated, and in 1862 locomotive construction and maintenance was done at the Crewe Locomotive Works, carriage building was done at Wolverton and wagon building was concentrated at Earlestown.
At its peak just before World War I, it ran a route mileage of more than 1,500 miles, and employed 111,000 people. In 1913 the company achieved a total revenue of £17,219,060 (equivalent to £1,664,280,000 in 2018) with working expenses of £11,322,164 (equivalent to £1,094,320,000 in 2018).
The LNWR became a constituent of the London, Midland and Scottish (LMS) railway when the railways of Great Britain were merged in the grouping of 1923. Ex-LNWR lines formed the core of the LMS's Western Division.
Nationalisation followed in 1948, with the English and Welsh lines of the LMS becoming the London Midland Region of British Railways. Some former LNWR routes were subsequently closed, notably the lines running East to West across the Midlands (e.g. Peterborough to Northampton and Cambridge to Oxford), but others were developed as part of the Inter City network, notably the main lines from London to Birmingham, Manchester, Liverpool and Carlisle, collectively known in the modern era as the West Coast Main Line. These were electrified in the 1960s and 1970s, and further upgraded in the 1990s and 2000s, with trains now running at up to 125 mph. Other LNWR lines survive as part of commuter networks around major cities such as Birmingham and Manchester. In 2017 it was announced that the new franchisee for the West Midlands and semi-fast West Coast services between London and North West England would utilise the brand London Northwestern Railway as an homage to the LNWR.
Illustration of a LNWR passenger locomotive, c. 1852
The LNWR's main engineering works were at Crewe (locomotives), Wolverton (carriages) and Earlestown (wagons). Locomotives were usually painted green at first, but in 1873 black was adopted as the standard livery. This finish has been described as "blackberry black".
On 2 September 1861 a ballast train came out of a siding onto the main line just past Kentish Town Junction without the signalman's permission, and an excursion train from Kew ran past the signals and collided with it, resulting in the deaths of fourteen passengers and two employees.
On 29 June 1867, a passenger train ran into the rear of a coal train at Warrington, Cheshire due to a pointsman's error which was compounded by the lack of interlocking between points and signals. Eight people were killed and 33 were injured.
On 20 August 1868, a rake of wagons ran away from Llandulas, Denbighshire during shunting operations. The wagons subsequently collided with the Irish Mail at Abergele, Denbighshire. Kerosene being carried in the wagons set the wreck on fire. Thirty-three people were killed in what was then the deadliest rail accident to have occurred in the United Kingdom.
On 14 September 1870, a mail train was diverted into a siding at Tamworth station, Staffordshire due to a signalman's error. The train crashed through the buffers and ended up in the River Anker, killing three people.
A section of the former L&NWR line and station buildings are preserved at Quainton near Aylesbury. It is administered by the Buckinghamshire Railway preservation Society and houses some original L&NWR rolling stock in the former Oxford Rewley Road station. It regularly runs steam trains using various locomotives.