Guillermo Willy Lamarca (born Buenos Aires, 1949) is a former Argentine rugby union player and a current coach.
He moved to Jockey Club of Salta, in 1972, where he was player and coach from 1972 to 1976.
He played there until 1978, when a serious injury forced him to leave competition.
He became coach of Tucumán Rugby Club in 1978, moving the following year to Lawn Tennis, where he was winner of the National Championship, in 1980 and 1981.
The duo led the "Pumas" at the 1991 Rugby World Cup, but weren't able to avoid the elimination after the 1st round.