ImpreMedia, which publishes both papers, said the appointment marked his return to the chain. In 2005, Keoseyan became director of Primera Hora, the Puerto Rican tabloid.
"It's great to have Ruben back at ImpreMedia. He is a terrific media executive and the right leader to take La Raza to new highs," ImpreMedia Chairman and CEO John Paton said in a statement.
Keoseyan first joined ImpreMedia in 2000 as managing editor of La Opinion, the nation's biggest Spanish-language daily. He was promoted to executive editor in 2004.
Keoseyan, who was born in Mexico City, began his career as a journalist for Televisa, the largest television network in Mexico. He was news director and anchor for KSBY, an NBC affiliate, on the first Spanish-language newscast in California's Central coast.