Construction began in 1850 and the line opened from New Haven to the Connecticut River in Old Saybrook on July 1, 1852.

The line west from Stonington opened December 30, 1858, ending at Groton, with another car ferry across the Thames River to New London.

This completed the "Shore Line" route between New York City and Boston; through passenger service began December 12, 1859, with night trains first running August 19, 1861 and sleeping cars November 11.

In 1864 the NYP&B bought the part east of New London, and the rest was reorganized as the Shore Line Railway.

In 1969 the New Haven merged into Penn Central, and then at the latest the Shore Line was extended along the whole New York City-Boston route.