Bow, McLachlan and Company of Paisley in Renfrewshire, Scotland built her in 1890 for the IBEAC. She was a "knock down" vessel; that is, she was bolted together in the shipyard at Paisley, all the parts marked with numbers, disassembled into many hundreds of parts and transported in kit form by sea to Kenya for reassembly. However, once the kit reached the port of Mombasa there was a delay and it remained there in storage until 1895, when ownership of the kit passed to the newly founded Uganda Railway. Construction of the railway westwards from Mombasa began in 1896. The kit was brought out of storage and taken to Kisumu on the shore of Lake Victoria, where assembly began in 1898.William Mackinnon was launched in 1900 and completed in 1901, the same year as the Uganda Railway branch to Kisumu was completed.
In the First World WarWilliam Mackinnon was armed as a gunboat. In 1929 she reached the end of her working life. She was withdrawn from service, taken out into deep water and scuttled.