Castle Cary railway station is on the Reading to Taunton line 115.25 miles (185.48 km) south west of London Paddington and the Bristol to Weymouth line 47.75 miles (77 km) south of Bristol Temple Meads. The two routes share tracks between Westbury and Castle Cary stations and are both operated by Great Western Railway, which also manages the station. The station is 1 mile (1.6 km) north of the market town of Castle Cary and 5 miles (8 km) south of Shepton Mallet in a largely rural area of Somerset, England.

Castle Cary station was originally on the Wilts, Somerset and Weymouth Railway, a railway that linked the Great Western Railway (GWR) at Chippenham with Weymouth. The line was authorised in 1845, was acquired by the GWR in 1850, reached Castle Cary on 1 September 1856, and was completed throughout in 1857.

For the remainder of the 19th century, the GWR's principal route from London Paddington station to Exeter, Plymouth and Penzance was an indirect one via Bristol Temple Meads (the so-called Great Way Round). However, in 1895 the GWR directors announced that new lines were to be constructed to enable trains to reach Exeter, Plymouth and Penzance in a shorter time. The first stages involved improvements to the Berks and Hants Extension Railway and the Wilts, Somerset and Weymouth Line which reduced the distance from London to Castle Cary by 14.25 miles (23 km) and provided double track throughout.

This was followed by the construction of the Langport and Castle Cary Railway, which was opened from Castle Cary to the existing Bristol to Exeter line at Cogload Junction in 1906. This transformed Castle Cary from a station on a secondary north to south line, to one on a main east to west route. The route resulting from these improvements and extensions forms the current London to Penzance line.

The station was awarded the Small Station of the Year award in the National Rail Awards 2007.

The station has three platforms. The main station facilities are located on the London bound platform 1, as well as the main station building and ticket office which is staffed until the afternoon. Toilet facilities are available on the concourse too. In front of the building is a car park for 100 cars, a bus stop and a taxi rank. Platform 2 serves west bound services to Taunton, Exeter, Plymouth and Penzance, whilst the shorter platform 3 can only be used by trains on the Bristol to Weymouth line. Immediately to the west of the station the Weymouth line diverges from the London to Penzance Line.

Castle Cary station is the closest station to the site of the Glastonbury Festival, which is held near Pilton about 8 miles away. During the period of the festival additional trains are provided, and special buses are run from the station to the festival site. The station also serves events at the Royal Bath and West Showground, though these are not provided with extra trains. It is also the nearest main line station to the city of Wells which lost its rail connection in 1963.

The Great Western Railway service between London Paddington and Exeter St Davids runs approximately every two hours, with 9 trains towards London Paddington per day, and 10 trains towards Exeter St Davids, although some services will reach stations such as Paignton and Plymouth. The service between Gloucester and Weymouth runs on a similar frequency, with 9 trains in each direction all weekdays except Friday, where only 8 operate northbound, however, some trains only operate between Bristol Temple Meads and Weymouth.

The South Western Railway service between London Waterloo and Yeovil Junction via Westbury and Salisbury is more irregular, however, as there are 6 trains towards London Waterloo throughout the day, but only 3 towards Yeovil Junction.

Preceding station	National Rail			Following station
Taunton		Great Western Railway Reading to Taunton Line		Westbury
Yeovil Pen Mill		Great Western Railway Heart of Wessex Line		Bruton
Yeovil Pen Mill		South Western Railway Heart of Wessex Line		Bruton