Herdman specialised in painting portraits and Scottish historical subjects, but also produced some notable landscapes in watercolour. He was a student of Robert Scott Lauder at the Trustees' Academy in Edinburgh and was encouraged to draw from nature. He was also strongly influenced by Lauder's admiration for the rich colour of Venetian painting and travelled to Italy at least twice. Herdman chose to stay in Edinburgh rather than move to London and established a successful practice. He was elected to the Royal Scottish Academy in 1863.