An American, born in Kansas City, Missouri, MacKenzie and his wife Alix lodged at the Leach Pottery cottage, and for a period of two years learned from Bernard LEACH the techniques of throwing that had been lacking in their previous training (at the Art Institute of Chicago).  From this apprenticeship experience they developed their own functional designs and standard ware.  Returning to the USA, they built a two-chambered climbing kiln in their workshop at Stillwater, Minnesota while the ceramist took up a lectureship at the University of Minnesota in 1953.  Alix worked alongside her husband in every respect until her death in 1962.

Warren progressed to Full Professor of Ceramics at Minnesota, and is now Emeritus Professor.  Warren still uses an adaptation of the wheel originally built for the St Ives pottery by Dicon NANCE.  He is quoted as saying that 'without Bernard's pioneering leadership, pottery made by the individual craftsman would not have realised the acclaim it enjoys today', and he continues to remember Leach, Shoji HAMADA and YANAGA as providing him with his springboard to the future.

Considered today as one of the most distinguished potters of his generation, honours and retrospective exhibitions abound.  His teaching is also available by video on the Internet.