The Portsmouth to Brighton Railway was built by the London, Brighton and South Coast Railway and its immediate predecessor in several stages.
The London and Brighton Railway built a branch line from Brighton to Shoreham, an important seaport. The branch opened in 1840. Under the London Brighton and South Coast Railway the line was extended progressively to Portsmouth, reached in 1847. The London and South Western Railway had a roundabout connection to Portsmouth, and the final route section on Portsea Island was operated jointly with the LSWR. Although the LBSCR coast route connected many important resorts, the trunk route from London to Portsmouth was commercially dominant, and the LSWR acquired the Portsmouth Direct Line, which was a better and shorter route. The LBSCR took steps to improve its own route, but it never became fully competitive with the LSWR for London traffic.
The line became the stem of several branch lines, as holiday travel, and later residential travel rose in importance, equalling agriculture and light industry. From 1906 steam railmotors were used in connection with new halts, simple low-cost passenger stations, and in 1937 the line was electrified on the third-rail system as part of an ambitious modernisation scheme implemented by the later Southern Railway.
Although some of the inland branches have closed, the coastal route and most of the coastal connections continue in use at the present day. A busy passenger train service operates on the line, including through journeys to the adjacent line to Southampton, under the branding West Coastway.