Bramhope Tunnel is on the Harrogate Line between Horsforth station and the Arthington Viaduct in West Yorkshire, England. Services through the railway tunnel are operated mainly by Northern. The tunnel was constructed during 1845–1849 by the Leeds and Thirsk Railway. It is notable for its 2.138-mile (3.441 km) length and its Grade II listed, crenellated north portal. The deaths of 24 men who were killed during its construction are commemorated in Otley churchyard by a monument that is a replica of the tunnel's north portal.

Thomas Grainger was the engineer for the line and James Bray the contractor. Two sighting towers were erected and 20 shafts sunk along the tunnel's line. Men excavated rock from the shaft faces until the shafts were connected and the tunnel was completed in 1848. Thousands of navvies lived locally in temporary bothies with their families, and worked in dangerous and wet conditions to facilitate the grand opening in 1849.

In the mid-1840s Railway Mania was taking hold and railway companies competed with each other to bring forward schemes to access Wharfedale. Most of these schemes did not come to fruition but the Leeds and Thirsk Railway Company's proposal, a counter to George Hudson's "megalomania", to build a line from Leeds to Thirsk received approval in the Leeds and Thirsk Railway Act 1845 (8 & 9 Vict. c. civ). The line would open up trade in Leeds to the North East and access lower Wharfedale. Among the several major obstacles on the route was the ridge between Airedale and Wharfedale requiring a long tunnel between Horsforth and Arthington under Bramhope village. The company appointed Thomas Grainger as engineer for the project and James Bray was the contractor for the Bramhope contract. Bray, of Black Bull Street in Leeds, was originally a brass and iron founder.

Water was taken at first from the town well opposite St Giles' Church, but the excessive demand diminished the supply and spoiled its quality. The tunnellers' water was then pumped from a site near the Dyneley Arms crossroads. At the same time the tunnel was draining away the local farmers' natural water supply and the source of Bramhope town well. Litigation on this subject continued for some years. To mitigate the situation, a public waterworks scheme with a reservoir and an aqueduct was proposed but not implemented.

The tunnel was planned to be 3,344 yards in length but during construction it was extended to 3,743 yards. The cost of building the whole line was estimated to be £800,000 but the final total rose to £2,150,313 (equivalent to £236,220,000 in 2025) by 1849 because of costs incurred for labour, unforeseen extra costs for tunnelling at Bramhope and work in Leeds and on the Arthington Viaduct. At a shareholders meeting in September 1848 it was reported that only 100 yards of new ground were left to be penetrated and Bray stated it would be possible to run a locomotive through the tunnel in the following May.

Work on the tunnel cost the lives of 24 men. The grand opening was 9 July 1849, a week later than intended, but the first train, full of Leeds and Thirsk railway officials, pulled by Bray's locomotive Stephenson, went through a few weeks earlier on 31 May. The railway was opened to the public on 10 July. When built it was the third-longest rail tunnel in the country. The Leeds and Thirsk Company was renamed the Leeds Northern Railway shortly after the line was completed.

Since 2016 most services on the line through the tunnel are operated by the Northern franchise on behalf of Rail North which represents the local transport authorities in West and North Yorkshire and other parts of the North of England.

Two sighting towers were built at a cost of £140 for the surveyors to keep the line true, then from 20 October 1845 twenty shafts were sunk to enable tunnelling. Tunnelling started after the foundation stone was laid at the bottom of No. 1 airshaft in July 1846. The separate working faces were joined into a single tunnel on 27 November 1848, and work was completed in summer 1849.