It had been working the nominally independent Cornwall Minerals Railway lines, in particular the passenger route from Par to Newquay, for some years and in 1896 it acquired that network by purchase.

The new line was to run from a triangular junction (Blackwater Junction) near Chacewater, 6 miles (10 km) west of Truro, and run via St Agnes and Perranporth to Shepherds; here the new route joined the existing Treamble goods and mineral branch, originally built by the Cornwall Minerals Railway.

The branch from there to Newquay was rebuilt for passenger operation, including a short alteration to eliminate a sharp curve, the Trevemper Deviation.

[3][4] At first the passenger stations were St Agnes, Perranporth, and Shepherds, but six halts were opened on 14 August 1905, partly in connection with the GWR's adoption of railmotors, integrated self-propelled coaches suited to lightly used local services.

The line was single between Blackwater and Tolcarn junctions with passing loops at the stations; it had a 40 mph (64 km/h) speed limit.

The low population density encouraged the GWR to introduce the new railmotors it had developed, and from 1905 several halts were opened with minimal facilities, to enable a low-cost service outside the principal holiday period.

On summer Saturdays there was a through train from Perranporth (08:15) to Paddington (arrive 15:55), calling only at St Agnes, Truro (set down), St Austell and Par (both pick up only); in the down direction the 08:25 Paddington train, making more conventional stops, conveyed a Perranporth portion, arriving at 16:20.

[2] On 9 November 1924 the branch was extended back to Chacewater station, parallel to the main line, enabling Blackwater (East) Junction signalbox to be abolished.

It had a single platform with a pagoda shelter, located in a cutting on the right hand side of trains going towards Newquay.

[9] Local dissatisfaction was expressed that the halt was some distance from the community served, the ground formation at Trevellas Coombe having prevented a closer approach.

[2] After closure, the sectional concrete platform was removed and installed The Dell, subsequently renamed Falmouth Town railway station on the Maritime Line.

The halt and adjacent road bridge survived until 1983 when most of the formation of the railway was obliterated and the cutting filled in.

[7] Shepherds station (Cornish: Bugel) A branch from Newquay to Treamble had been opened by the Cornwall Minerals Railway on 1 June 1874.

[8] The platform and waiting shelter may still survive amongst the undergrowth just across the road from the terminus of the Lappa Valley Railway, but are now inaccessible.

It had a single platform on the right of trains heading towards Newquay and was situated just west of the level crossing, east of which a siding was provided until 5 September 1948.

[5] Trevemper Siding served an industrial factory; it was on a short section of the Treffry Tramways route that was by-passed when the main line was improved.

[7] Treloggan curve had been taken out of use in 1888, but it was reinstated in 1931 for the purpose of turning engines when the station turntable was abolished to enable enlargement of the siding facilities.

It continues to serve Atlantic Coast Line trains from Par and a number of long-distance services on summer Saturdays.

Leaving Chacewater it climbed at 1 in 72 / 1 in 60 to Mount Hawke; it descended from St Agnes at 1 in 60 / 1 in 99, steepening to 2 miles (3 km) at 1 in 51 / 1 in 47 after Mithian.