Born in the Lancashire coastal town of Blackpool, Smith was educated at the University of Manchester where he obtained his PhD in 1956. He moved soon after to Canada working initially as a postdoctoral fellow at the University of British Columbia, Vancouver. From 1961 until 1966 Smith served with the Fisheries Research Board of Canada, Vancouver, but returned to the University of British Columbia in 1966 and was appointed professor of biochemistry in 1970.

In 1978 Smith introduced a basic new technique known as ‘site specific mutagenesis’ into molecular biology. In order to establish the function of a particular protein or gene, it had long been an established procedure to induce a mutation in the gene and observe the consequences. Thus if changes to a gene prevented an organism from making a particular enzyme, then it was reasonable to conclude that the gene controlled some part of the production of that enzyme. The difficulty with this approach was that the available mutagens, radiation and chemicals, produced random and multiple mutations. The precise effects of a single mutant gene could seldom, therefore, be distinguished from the other consequences of the mutagens.

Smith demonstrated how to introduce specific mutations into genes. He worked with a single strand of viral DNA. A short segment of complementary DNA differing at a single site was assembled and allowed to bind to the original viral DNA. The second strand was then completed in the normal way and the double-stranded DNA inserted into the viral genome. The virus would develop with normal and mutated versions of the gene which would in turn produce normal and mutated proteins. When the different protein molecules were compared, the role of the initial mutation would become apparent.

The new technique was widely used in protein chemistry and molecular biology. Smith himself has used it to investigate the role of cytochrome c in cellular respiration, and myoglobin in oxygen storage.

For his work in this field Smith shared the 1993 Nobel Prize for chemistry with Kary Mullis.