รฟท., RTGS: kan rot fai haeng prathet thai) is the state-owned rail operator under the jurisdiction of the Ministry of Transport in Thailand.

Construction of the Bangkok-Ayutthaya railway (71 km or 44 mi), the first part of the Northern Line, was started in 1890 and inaugurated on 26 March 1897.

[9] In the fiscal year ending 30 September 2016, the military government budgeted 7,600 million baht for SRT infrastructure investments to be used for track duplication, an extension of Bangkok's elevated railway, and construction of bridges, fences, and track improvements, however, the SRT had managed to disburse only 53 percent of its allotted investment budget of 60 billion baht, compared with an average disbursement rate of 80 percent by Thailand's other 55 state-owned enterprises (SOEs).

[11] "If you look at the SRT they are a bit like a patient in [intensive care] and everyone is saying to him 'you are the future' and trying to kick him out of bed when he is still moaning and groaning," said Ruth Banomyong, a logistics and transport expert at Thammasat University.

[13] Under the auspices of the Transport Ministry, the SRT has submitted a rehabilitation plan that will be presented to the State Enterprise Policy Commission on 30 July 2018.

Hopewell Holdings of Hong Kong was the lead contractor for SRT's ill-fated Bangkok Elevated Road and Train System.

On 23 April 2019, Thailand's Supreme Administrative Court upheld an arbitration committee's ruling in favour of Hopewell.

[19] To address a long list of complaints accusing SRT of a lack of transparency in bids for projects and procurement deals, Prime Minister Prayut Chan-o-cha fired the governor and board of the State Railway of Thailand in February 2017, using his special powers under Section 44 of the interim constitution.

There, it splits from the Northeastern Line and proceeds through Lopburi, Nakhon Sawan, Phichit, Phitsanulok, Denchai, Lampang, Lamphun, before finally reaching Chiang Mai, 751 km (467 mi) from Bangkok.

Then at Thanon Chira Junction, the line splits with one route passing Khon Kaen and Udon Thani before terminating at Nong Khai 624 kilometers (388 mi) from Bangkok.

The other route passes through Buriram, Surin, Sisaket to reach Ubon Ratchathani, 575 km (357 mi) from Bangkok.

The Southern Line itself continues southbound through Ratchaburi, Phetchaburi, Hua Hin, Prachuap Khiri Khan Province, Chumphon, to Surat Thani 678 kilometers (421 mi) distant.

The main line from Nakhon Sri Thammarat continues through Phatthalung before reaching Hat Yai Junction in Songkhla Province.

From here, a line branches to connect with the Malaysian railway at Padang Besar and the mainline continues to Su-ngai Kolok passing through Yala Province.

The line begins at Wongwian Yai in Bangkok before terminating at the Mahachai station in Samut Sakhon, where a ferry is used by passengers to cross the Tha Chin River.

[24] SRT has also historically allowed operation of the Eastern and Oriental Express on their tracks which runs from Singapore to Bangkok and vice versa, although trips in 2024 did not enter Thailand.

In 2024, long distance overnight train services between Bangkok and Vientiane Khamsavath railway station were started.

The rail link to Cambodia via Poipet from the railhead at Aranyaprathet was constructed in 1941, but was closed in 1961 due to strained Thai-Cambodian relations during the Cold War.

[38] In an attempt to increase the railway's share of the nation's freight transportation market, in 2016 the SRT, in a joint project with Japan, started experimenting with small, 12-foot containers.

Refurbished old KiHa 183 trains debuted on the SRT network, gifted by the JR Hokkaido Railway Company, are now some of the most popular excursion train services, providing day and overnight tours to different provinces such as Ayutthaya, Hua Hin, Chacheongsao, Nakhon Nayok and Nam Tok Sai Yok Noi.

As of August 2019, the SRT board announced that the unique vanilla and maroon paints scheme would be replaced in the reconstructions of the stations with designs that "reflect local identities".

[55] Japan would provide Shinkansen technology for a high-speed rail link between Bangkok and the northern city of Chiang Mai.

Seven stations are planned for this segment: Bang Sue, Don Mueang, Ayutthaya, Lopburi, Nakhon Sawan, Phichit, and Phitsanulok.

[56] The Thai government announced in September 2019 that it may cancel Bangkok-Chiang Mai high-speed rail project after private investors declined to invest.

During 2017, OTP and the Ministry of Transport in consultation with the SRT agreed that by extending the line to terminate at Don Mueang it would effectively include the long delayed extension of the Airport Rail Link (Bangkok) from Makkasan Station to Don Mueang Airport as part of the project.

In early-2018, the section to Rayong was excluded due to environmental and safety concerns and it was decided that the line would terminate at U-Tapao Airport.

[66] The Charoen Pokphand (CP) Group-led consortium consisting of Italian-Thai Development, China Railway Construction Corporation Ltd, CH.

[67] The project was eventually approved in October 2019 as a public private partnership between the Thai government and Charoen Pokphand/China Railway Construction Corporation.

China would conduct feasibility studies, design the system, construct tunnels and bridges, and lay track.

Construction of Thailand's 873-kilometre-long portion of the railway system started in December 2017[71][72] and the Phase 1 line is due to open in 2023.