This was announced in a press statement issued by the Urban Redevelopment Authority (URA) and the Preservation of Monuments Board (PMB) yesterday.
The two stations are now managed by Malaysian train operator Keretapi Tanah Melayu (KTM), which runs services from Tanjong Pagar to Kuala Lumpur daily.
Trains no longer stop at the Bukit Timah station in Blackmore Drive.
The prime ministers of Singapore and Malaysia had announced at their retreat here on May 24 last year that train services to Malaysia will be relocated to the Woodlands Train Checkpoint by July 1.
Under a land swop agreement inked in September last year, Malaysia will get six land parcels in Marina South and the Ophir-Rochor area in exchange for giving up six railway land sites in Tanjong Pagar, Kranji, Woodlands and Bukit Timah.
In the joint statement, the URA and the PMB said the decision was made in view of the stations' 'deep historical significance and to protect physical reminders of our rich heritage'.
The Tanjong Pagar station joins the 63 buildings already listed as national monuments, among them the former St Joseph's Institution (now the Singapore Art Museum) and St James Power Station (now a nightlife hub).
The form and facade of a building gazetted as a national monument has to be kept unchanged, though the interior can be altered on a case-by-case basis.
For conserved buildings, only the front needs to be preserved. The side and back, as well as the interior, can be amended or extended with URA's approval.
The land use for the plots housing the Tanjong Pagar and Bukit Timah stations will be reviewed only at year end, under the URA's Concept Plan.
Still, the move to keep the stations is 'a very good start', said Ms Dahlia Shamsuddin, the acting president of the Singapore Heritage Society. She added that the Government should impose strict controls to ensure that the two stations are not dwarfed by surrounding developments, noting that the Keppel viaduct currently runs right in front of the Tanjong Pagar station.
Dr Chua Ai Lin, a National University of Singapore historian, agrees. 'I hope the stations will be conserved in a way that preserves the dignity and history of their former use,' she said, adding that the Tanjong Pagar station is an important reminder of Singapore's long history as part of British Malaya.
The station in Bukit Timah is also symbolic because it helped to bring Singaporeans closer to each other, she added.
Tanjong Pagar Railway Station opened in 1932. A few smaller stations were also built to serve the suburban parts of Singapore: Alexandra, Tanglin Halt and Bukit Timah stations. Only the latter still stands.
Mr Ho Weng Hin, 36, director of Studio Lapis, an architectural conservation specialist consultancy, hopes the two stations will not become 'another bland shopping mall or exclusive entertainment nightspot': 'In particular, the Tanjong Pagar station, with its soaring passenger hall, could become an exhibition gallery or a grand hall for a museum, like Musee d'Orsay in Paris.'
The announcement yesterday also pleased IT firm manager Carolyn Seet, who started a petition in July to retain the Tanjong Pagar station as a transport museum.
The 38-year-old, who has garnered more than 650 signatures online, will send her petition to the Prime Minister's Office once she gathers 1,000.
'I am obviously very happy but my concern is that it may be turned into another hotel or a place not open to the public,' said the mother of two.
