The initial interest was for a 3.9-kilometer (2.4 mi) long line to the southwestern end of the lake Rore to the town center.

[3] In 1874, Aust-Agder County Municipality (then Nedenes) established a railway committee as a response to the national ambitions of creating a Vestland Line (later named the Sørland Line) which would connect Rogaland and Agder to Oslo and Eastern Norway.

In Nordenes, it was proposed that both Arendal and Grimstad would have a branch line, which would connect somewhere north of towns, and continue northwards into the interior.

Originally the proposal had called for the branching to occur even closer to the coast, at Rykene.

The proposed line would have branches to Skien, Kragerø, Arendal, Åmli, Risør, Grimtad, Tvedestrand and Notodden.

In a meeting for various local politicians on 20 May 1895, it was decided to create a committee which was given permission to apply for a concession to build a railway.

Two days later, at a new meeting, the committee was given permission to extend the line to Blakstad Bridge.

[6] Parliament voted on 20 May 1899 to give a grant of 368,000 to the Grimstad Line if it received concession.

The proposal was passed with 71 against 36 votes, with the minority arguing that it would upset the balance in the compromise which had been made in 1894 for a series of railway lines throughout the country.

[6] The rolling stock would be the same, with the Grimstad Line needing two locomotives, six carriages with a total 114 seats, four boxcars and thirty lumber cars.

In January 1900, Krum launched four plans for the station in Grimstad, all which would involve it being located at the port.

After much local debate, the municipal council on 20 June 1902 with 25 against 3 votes chose to locate it at Vestrebugt.

[8] There were four bids for the tender to build the line; Ingeniørfirmaet Strøm & Hornemann was the cheapest and was awarded the contract in June 1903.

They started work in 1903, despite that a concession was not granted until 29 August 1904, with a duration of 30 years, on condition that the line be completed by 1907.

[11] The line was finished on 23 June 1907, when the first train, with the municipal council and their wives, ran from Grimstad to Rise.

In June 1908, the company Aksjeselskapet Grimstad–Frolandsbanen was incorporated, with two board members appointed by Grimstad Municipal Council and two by the general assembly.

The factory at Rykene also chose to build an aerial tramway to transport its wood pulp instead of sending it via the railway.

An extraordinary general assembly was held on 30 November 1911 where the company was decided dissolved and the assets transferred to the state.

After being nationalized, NSB stationed a telegraph operator at Rykene, and increased the number of ties to increase the axle load to NSB's standard of 5.5 tonnes (5.4 long tons; 6.1 short tons).

In preparation for the arrival, NSB had in 1923 proposed to convert the Treungen and Grimstad Lines to standard gauge.

The affected municipalities all issued statements opposing the closing and Grimstad stated they the NOK 90,000 in local funding for the Sørland Line would not be given.

They also stated that if the line was closed, a series of improvements to the local road network would have to be made.

The right-of-way had to be changed at the northern section before the bridge across Nidelva, giving the line a 128-meter (420 ft) curve radius.

[20] During ten hours on 8 November 1936, the 24 switches were replaced, and the following day operations resumed, with standard gauge trains.

[23] Class 9 locomotives were introduced on so-called "small trains", where the fireman also acted as conductor.

In a letter dated 28 May, NSB proposed closing the line from 1 October 1958, and received support from the Ministry of Transport and Communications.