Roberts was born in [[Groes]], [[Denbighshire]], Wales to William Roberts, a farmer. Although he spent some years of his childhood there, he later moved to [[Liverpool]]. There, he became an apprentice to John Johnson & Son (which later became Johnson and Robinson), a firm of mechanical engineers, for 7 years beginning on 12 November, 1844. He became a partner in 1847, and supplemented his job with night school. When Peter Robinson died in 1855, Roberts was made manager of the firm. When the other partner, John Johnson died, Roberts was in charge of the contracts and affairs of the firm. Roberts began working as a builder in 1859, and was joined by Peter Robinson's son, J. J. Robinson, in 1862. He was very successful, and became known as one of the best [[engineer]]s in the region.
Isaac Roberts married his first wife, Ellen Anne, in 1875, making him the son-in-law of Anthony Cartmell. Isaac Roberts married [[Dorothea Klumpke]], who was nearly 30 years his junior, in 1901.
