From an early age he was a close friend of Edward Atkinson Hornel and would often bring in New Year with him in Kirkcudbright.
Within the architectural profession, he was closest to John Archibald Campbell, and is credited with training Charles Rennie Mackintosh.
[4]: 45 Mackintosh was made partner in 1901, and Keppie returned to design, producing a series of Scots Renaissance buildings throughout Glasgow.
[1] Keppie was elected to the Royal Scottish Academy in 1920, and continued to take an active role in professional matters, particularly as a governor of the Glasgow School of Art.
He endowed the John Honeyman Studentships in architecture and in Sculpture in 1923, and did much to promote the career of Benno Schotz.