But Arnott's senior football career would begin in 1882 at the age of twenty--one with a move to Queen's Park. He is said to have arrived as the replacement of Andrew Watson, which seems unlikely. Whilst Watson could play on either side he was largely at right-back for club and country. Arnott was originally a left-back. Andrew Hair Holm was the Queen's Park left-back at the time but could also play on either flank and, when Watson did move on, he simply stepped across allowing Arnott in. 

From that point, however, Wattie's rise was meteoric. He won his first caps in 1883 and alongside Hair Holm. He first played against England in 1884, incidentally at right-back, having just captained the national team against Ireland. However, whilst at national level Scotland prospered, at club level Queen's Park struggled somewhat. Between 1882 and 1886, when he was actually partnered at full-back by a returned Watson, they reached the Scottish Cup Final only once, the walk-over of 1884. And they would not do so again until 1890, by which time Scottish football was changing and Arnott was almost thirty. In fact, having briefly retired in 1888, he would play on until 1893 with Queen's Park until he fell out with the club over being dropped and then turned out for Edinburgh club, St. Bernard's, for another season. 1893 would also be the year of his last cap, a 5-2 gubbing by England, where, with the English left-winger, Fred Spikesley, scoring two late goals, both Arnott's age and his style of full-back play from an earlier era were exposed. 

Throughout Arnott's golden footballing years he had worked first as a clerk, turning by the end of his playing career to quarrying and then the building materials' trade more generally, as a merchant and/or a contractor's agent. It would be work that would take him briefly to Belfast in 1891 and then, as a quarry foreman, to Kirkpatrick-Fleming in Dumfriesshire. There he met and in 1896 married Mary Glendinning. They would have four children, three boys and a girl, in Dumfriesshire and then back in Glasgow, where they would settle first in Mount Florida and then in Clarkston. From there he would pursue his other sporting interests, bowls, cricket, tennis yachting and curling. And it would be still in Clarkston that Arnott would die at the age of seventy in 1931, Mary outliving him by two and half decades.