Born in Bristol in 1824, one of 13 children.
His father, Thomas Plimsoll, was an Excise Office clerk. When he died in 1844, Samuel, having started work at the age of 15, supported his mother and five of his younger siblings. Using a bequest, Plimsoll entered the coal transportation business but suffered mixed fortunes. In 1855 he was declared bankrupt, however, he eventually became prosperous with an office in London.
A well developed sense of social justice led him to stand for Parliament and he became MP for Derby in 1868 until 1880.
By the 1870′s, 3000 merchant seamen were being lost at sea each year and Plimsoll began to campaign vigorously for better safety regulation to deal with the deliberate overloading of merchant vessels by reckless and unscrupulous owners. After much acrimonious argument and debate in Parliament the Merchant Shipping Act of 1876 was passed requiring vessels to be marked with a load-line to indicate how much cargo could be safely carried.
In 1890 another Act empowered the Board of Trade to affix what had become known as the Plimsoll Line.
When he died in Folkestone in 1898 a contingent of sailors drew his hearse to his funeral and burial in St Martin’s Church, Cheriton, Kent.
In his birthplace of Bristol he is commemorated by a bust which formerly stood on the Portway near the entrance to the Floating Harbour, but it now stands opposite the SS Great Britain on Capricorn Quay.