Willie Dunn Jr was involved in several design and remodelling projects. The first of these were clubs where he was the professional and/or greenkeeper: Royal North Devon, Westward Ho! (current layout); Royal Epping Forest (revised by James Braid); Shinnecock Hills GC, NY (extension from 12 to 18 holes; later substantially redesigned). He also designed: Apawamis Club (NY); Ocean City (NJ) and Saranac Inn G&CC (with nephew Seymour Dunn).

Willie Dunn Jr was born in 1865 in Blackheath, London, while his father held the post of greenkeeper and club maker at Royal Blackheath GC. That year the family returned to Thistle GC in Leith, near Edinburgh. In 1881 Willie Jr moved to North Berwick where his older brother Tom (older by 15 yrs) was the head greenkeeper. Willie Jr branched out on his own as a greenkeeper and course designer, first at Royal North Devon (Westward Ho!) in southwest England, then at Royal Epping Forest, Chingford, near London.

He spent several winters in Biarritz, France where brother Tom designed the course. Willie Dunn Jr remained at Biarritz GC for six more years; while there he met William K. Vanderbilt, who persuaded him to journey to America. Dunn's first post was as golf professional at Shinnecock Hills GC, where he extended the existing 12 hole course to 18.

Willie Dunn Jr was the first unofficial champion of America in 1894, defeating another Scottish golfer Willie Campbell. A year later Dunn had to settle for second place in the first official US Open Championship. By 1896 Dunn had settled with his wife and son Norman at Ardsley CC in New York. It was here he set up a club manufacturing business and was joined by his nephew John Duncan Dunn (son of his brother Tom). He began experimenting with steel shafted clubs and was the first to use a tee peg. In 1895, he established the first Indoor Golf Centre in America.

Most historians agree that Willie Dunn Jr had an important influence on the development of golf in the United States in the early-1900s. He moved to San Jose, California in the 1920s, where he continued the design of new golf equipment. Willie Dunn died in 1952 in Putney, London, and is buried in Putney Vale Cemetery with a headstone inscribed "Willie Dunn Champion of America 1894."