The line was built in two stages by the South Eastern Railway (SER). The first stage opened on 24 September 1844 and was a branch off the SER's first main line that crossed Kent between the coast ports of Dover and Folkestone and the LBSCR's main line at Redhill. According to a contemporary report in "The Times" newspaper, the opening of the branch line was an attempt to convey hops and fruit traffic back to Maidstone, which was losing trade to various points along the Dover line. The junction was at Paddock Wood and followed the Medway Valley down to the county town of Maidstone that had been by-passed by the new main line. Twelve years later, on 18 June 1856 the extension of the line further down the Medway Valley was opened, to join the North Kent Line at Strood (which had opened in 1847). The extension was built by the railway contractor Edward Betts, who lived locally at Preston Hall and through whose estate the line partially passed. Betts arranged for his local station at Aylesford to be built in a much grander style than the other country stations along the line.