After Oxford, Nickalls joined
Leander, of which he was Captain in 1892 and 1897 and took the main prizes at Henley Royal Regatta over the next seven years. His Leander crew won the
Grand Challenge Cup in 1891 and 1892, and in 1891, he and Ampthill won Silver Goblets again. In 1893, he was in the Magdalen crew that won the
Stewards' Challenge Cup and won the Diamonds again against Kennedy. In 1894, he won Silver Goblets, partnering with his brother Vivian, whom he defeated in the same year in the Diamonds. Vivian Nickalls became a member of
London Rowing Club, and Guy joined them to win the Stewards in 1895, and the brothers also won Silver Goblets again that year. However, Guy lost Diamonds that year to
Rupert Guinness. In 1896, Nickalls had three wins – the Grand with Leander, Stewards with London Rowing Club, and Silver Goblets with his brother. In 1897 he won Stewards with Leander and Silver Goblets with E. R. Balfour. After a break of several years, Nickalls was a member of the Leander crew that won the Grand in 1905, but over the next few years, the dominant eight in the event was the Belgian crew from
Royal Club Nautique de Gand. Nickalls was a member of the winning crews in the Stewards in 1905, 1906 and 1907. In 1908, he was a member of the Leander
eight, which was assembled to challenge the Belgians
rowing at the 1908 Summer Olympics and beat them to win the gold medal for Great Britain. ==Later career==