[4] Upon completing his education, Johnston began his professional career by joining the shipping company of Robert MacAndrews & Co (based on London), with whom he was directly related through his maternal family.

[3] For around 30 years he remained in charge of supervising the activities of the company, which he managed with remarkable success, significantly increasing already relevant operations.

The oldest account of a sporting activity made by him can be found in 1878 aboard the Macareno boat in a regattas held on the Guadalquivir, next to Tablada, in honor of the Spanish royal family, who were visiting Seville.

[6][7] Due to Johnston's status in the city, he was elected the club's first-ever president, while another Scot, a native of Glasgow, Hugh MacColl, became the first captain.

[3][7] Among the agreements made by the club's founders on that historic evening, it was agreed that Sevilla FC should play under the rules of the English FA.

[5][1] A few weeks after founding the club, on 25 February 1890, Isaías White Méndez, the then secretary of Sevilla FC, wrote a letter to the Huelva recreational club to invite them to play a football match in Seville, which took place on 8 March 1890 at the Hipódromo de Tablada, a horse racing track, with Seville winning 2–0.

[5] In an interview with a Huelva newspaper in 1933, Daniel Young, a worker at Rio Tinto Co., stated that "Mr. Johnson" was almost always the referee of their matches.

[5] Years later, in January 1908, Johnston, who was still in Seville, refereed another match between Sevilla FC and Receativo de Huelva in La Tablada, which ended in a 4–0 win to the locals.