It runs from Ashford, Kent via Romney Marsh, Rye and the Ore Tunnel to Hastings where it connects to the East Coastway line towards Eastbourne and Brighton.

The SER clashed with the rival London, Brighton and South Coast Railway, leading to disputes over the route, planning and operation.

[21] Ham Street, Appledore and Rye have staggered platforms; passengers could originally cross the line between them, but this was disallowed for safety reasons.

The South Eastern Railway (SER) wanted to construct a line between Headcorn, Rye and Hastings, but the Parliamentary Select Committee thought there would be insufficient traffic.

[28] The two companies reached a compromise, by which the BLHR were authorised to build the line from Hastings to Ashford, with a caveat that the SER could take over operation if they wished.

The proposed line passed through countryside with only Rye as a significant settlement, so the SER easily persuaded the BLHR to hand over construction rights.

[29][30] As part of the contract, the SER had to pay £10,000 towards refurbishing Rye Harbour, and took responsibility for drainage of the Royal Military Canal which ran close to the line along Romney Marsh.

[31] On 27 July 1846, the LBR and BLHR amalgamated with several other lines to form the London, Brighton and South Coast Railway (LB&SCR).

[29] The SER were unhappy about the proposed line from Rye to Hastings via Ore, which they viewed as too expensive compared to the alternative route via Whatlington.

[36] The line was planned to be opened on 28 October 1850 by Thomas Farncombe, Lord Mayor of London, who inserted the last brick in both the Ore and Mount Pleasant tunnels.

[8] The dispute between the SER and the LB&SCR was not fully resolved until 5 December 1870, when the former was allowed to run trains to St Leonards Warrior Square.

[46] To make money and boost traffic on the line, the SER agreed to hold unlicensed boxing matches on Romney Marsh.

On 29 January 1856, a special train ran from London Bridge to Appledore for a prize fight between Tom Sayers and Harry Poulson.

[53] The SER had tenuous plans to build a cross-channel passenger ferry terminal at Dungeness, which would provide a dedicated route from London to Paris.

[13][9] Following World War I, plans were put forward to construct a chord linking the line eastwards at Ashford towards Dover Priory.

[67] It was revived for the Kent electrification scheme Phase 2 of the British Railways Modernisation Plan in the early 1960s, which included some preparatory work such as a footbridge at Rye.

[69][70] Like other lines threatened with closure, there was strong opposition, and the route survived because the nearby road network made it impractical to run a replacement bus service.

[72] The local member of parliament for Rye, Bryant Godman Irvine, made a significant Commons speech complaining about the decision to close the line.

[73][74] To save money and prevent closure, the main line was temporarily single-tracked between Appledore and Ore from June 1965, which lasted until September 1966.

[77][78] Shortly afterwards, John Morris, Parliamentary Under-Secretary of State for the Ministry of Transport, said that the remaining line was under review and would not close without further advice.

[84] On 31 July the following year, the ministry recommended the line for closure but stated that services would run indefinitely for the foreseeable future.

[81] The line was single-tracked between Appledore and Ore on 1 October 1979, leaving a passing loop at Rye, in order to reduce maintenance and operational costs.

[94] Norman Baker, MP for Lewes described a Marshlink service as "a 1954 diesel train, which shunts along like Thomas the Tank Engine at about 10 mph from Ashford to Hastings.

[96] The line closed for nine weeks between January and March 2012 for essential repair work to Ore tunnel, which was at risk of seeping water.

[118] Southern planned to withdraw this rolling stock after completing electrification of its remaining diesel lines, but the Strategic Rail Authority rejected the £150 million cost as prohibitive.

[125][126] This would require remodelling Ashford International to connect the Marshlink line to HS1, installing power systems, and adding a grade-separated diversion from Rye to the west, in addition to new trains.

They have reported that a high proportion of children and the elderly use the line compared to others in the south east, and a lack of additional rolling stock.

[72] In 2016, Rudd chaired a working group to look at short and long-term plans for upgrading the Marshlink line, including the potential accommodation of Class 395 rolling stock.

[132] In early 2021, Kent County Council wrote a strategic outline business case (SOBC) to the government for electrifying the line and track changes at Ashford.

[133] Later that year, Network Rail made two proposals; one with diesel bi-mode trains estimated at £153m – £198m, the other recommending third-rail electrification costed at £434m – £557m.