He missed out of securing a card in 2017 – losing a Q-school play-off – but then got his breakthrough in his rookie season with the 2018 Russian Open Golf Championship (Senior) before going on to win twice the next year, claiming the Sinclair Invitational and the Paris Legends Championship en route to a 3rd place finish in the Order of Merit.
More recently, he was runner-up in the 2022 Swiss Seniors Open event.
Aside from his three wins, David has registered 13 other top ten finishes on the Legends Tour.

In 2025, Shacklady continued to compete in various tournaments. Notably, he finished 8th at the Swiss Seniors Open in July, recording a score of 200 (−10).