Energetic politician and businessman. Born in Hull and educated there, he began his career in teaching but was offered the post of sub-editor of the Hull Advertiser after having had his letters published. This led to Leng's appointment as Editor of the Dundee Advertiser, where he restored its fortunes, increased its circulation and introduced new printing technology. He created new titles such as the Evening Telegraph and People's Friend, which both still exist. He gained control of the publishing company and also controlled Donside Paper Mills in Aberdeen, which supplied the paper for his newspapers. Leng became a wealthy man and stood for Parliament, serving as Liberal MP for Dundee between 1889 and 1905. He was a strong supporter of Home Rule with independent parliaments for Scotland, England, Wales and Ireland. He also brought forward legislation to improve the lives of women, children and war veterans, and reduce the working hours of railwaymen.
He was knighted in 1893, created a Deputy Lieutenant of Dundee the same year, and awarded an honorary doctorate by the University of St. Andrews in 1902. In 1905, Leng & Co merged another prominent Dundee publisher, Thomson's, under the leadership of D.C. Thomson (1861 - 1954), owners of the Dundee Courier, and the company went on to great success.
Leng lived at Kinbrae House in Newport-on-Tay, which was demolished c. 1960. He enjoyed travel, visiting the United States (1876), India & Ceylon (1896), the eastern Mediterranean (1897), Egypt & Sicily (1902) and the USA & Canada (1905), with each trip described by him in published volumes. He died in California while on another visit, and his cremated remains were returned to Scotland to be buried in the fine mausoleum he had created in the cemetery at Vicarsford in memory of his first wife, Emily (1829-94).
He is remembered as an enlightened employer who did much for Dundee and NE Fife. Leng created the Sir John Leng Trust in 1901, "to stimulate literary and scientific pursuits amongst the youth of Dundee" by awarding annual medals and prizes. His name also survives in the Thomson-Leng Musical Society.
