Weaver was born in Los Angeles, California on December 21, 1908. He was the son of actor/director Sylvester Laflin Weaver, Sr. (1874-1964) and actress Eleanor Isabel Dixon (1879-1966), Sylvester Jr.'s grandfather was Peter Laflin Weaver (1841-1912), a businessman, his great-grandfather was Henry Laflin Weaver (1808-1894), also a businessman, his great-great-grandfather was Charles Laflin Weaver (1708-1816), a manufacturer, Sylvester, Jr. died on March 15, 2002 in his home in Santa Barbara, California from natural causes, he was 93 years old.