Maclaren was born in Ormiston, Haddingtonshire, the son of a farmer and cattle-dealer. He was almost entirely self-educated, and when a young man became a mercantile clerk in Edinburgh.
In 1817, with John Ritchie, John Ramsay McCulloch and William Ritchie, he established The Scotsman newspaper in Edinburgh and at first acted as its editor for its first 27 years. Offered a post as clerk in the custom house, he resigned his editorial position, resuming it in 1820, and resigning it again in 1845. In 1820, Maclaren was appointed editor of the sixth edition of the Encyclopædia Britannica. From 1864-1866 he was president of the Edinburgh Geological Society, in which city he died in 1866. He was interred at the Grange Cemetery.