Samuel Johnson was born at Manchester, Lancashire, England, on 16 March 1827, the son of Thomas Johnson, a saddler, and his wife, Hannah Cope. On 5 June 1848 he married Thereza (Thirza) Mellor at Glossop, Derbyshire.
Johnson was educated in Manchester. After an apprenticeship in the printing trade he went into business on his own account in 1850, establishing a large and prosperous printing shop. His experience in journalism began on a daily newspaper in Manchester. In 1858 he transferred to Castleford, Yorkshire, where he took over as editor and proprietor of a local newspaper. In 1862 he joined the promoters of the Albertland settlement, a group of non-conformist idealists who proposed to emigrate to New Zealand to set up a model community. Johnson was appointed editor and printer to the venture and in 1862 embarked with his family (and a printing press) on the ship Matilda Wattenbach, arriving in Auckland on 8 September. During the voyage he produced two issues of the Albertland Gazette and Ocean Chronicle before his cases of type were spilt and hopelessly disarranged during a storm.
The venture selected a site, Port Albert, on an inlet of the Kaipara Harbour, but Johnson had fallen out with W. R. Brame, the settlement's leader, and remained in Auckland where he planned to set up his own business. He went briefly to Dunedin to work with his brother, Thomas, who was established there as a printer, but in March 1863 went to Port Albert. On 1 August 1863 he published the third issue (the first on dry land) of the Albertland Gazette, and continued to publish the Gazette at intervals until June 1864. He was his own publisher, editor, reporter, compositor and pressman, and in addition was postmaster, mail carrier and secretary to the settlers and to the trustees of the Port Albert Trust Estate. The settlement was not a success, and the community faded away as settlers left the district. In July 1864 Johnson put his house up for sale.
Johnson may have returned to Dunedin to work with his brother again, but by April 1866 he was in Blenheim where he and Thomas established the Marlborough Express, with a promise that the weekly newspaper would serve the interests of the whole province, rising above local rivalries. From early 1867 Samuel was sole proprietor of the paper. Despite his promise he vigorously supported W. H. Eyes and the Blenheim faction in the Marlborough Provincial Council. The Express prospered, with the help of a monopoly on government advertising, and increased its frequency to twice weekly in June 1871. When Eyes resigned from the provincial council Johnson stood for his Lower Wairau seat, and was elected in 1872. In 1874 he retired in disgust, he claimed, at the council's factious and petty parochialism.
After the abolition of the provinces in 1876 the Express supported Sir George Grey and liberal politics. Johnson continued his virulent editorial attacks on his chief competitor, the Picton-based Marlborough Press, and its conservative political allies. After the general elections of 1879 he was faced with five libel suits.
At the end of 1879 Johnson sold the Express and in 1881 visited England with his family. On his return he went to Waipawa, Hawke's Bay, where in 1884 he and his brother briefly ran the Waipawa Mail. In retirement he continued to work as correspondent to the Hawke's Bay Herald. At Waipawa he was appointed coroner in 1885, and his community activities included service on the local school committee and education board. He was was a long-time Freemason and active in the local Anglican church. He died at Waipawa on 6 August 1905, survived by his wife, two daughters and a son.