Mercado began his career as an actor in early Puerto Rican soap operas. He was one of the first Puerto Rican teen idols, and his fame soon reached all of Latin America.
During the 1960s, Mercado moved to India, where he began studying astrology. Upon returning to Puerto Rico, he landed a weekly astrology television show. Although the channel went bankrupt, Mercado's show soon moved to Tele Once (channel 11). He has had shows on Americann television at various times and, for a while during the late 1980s, he moved to Miami, Florida, where he became better known among the American public and people of other English-speaking countries.
In addition to his work for celebrities, Mercado also often does mall tours and goes to different places where people can hear him give out his predictions for free. Mercado's trademarks are his wildly colored capes, designer suits and sharp wit.
Mercado recently began writing horoscopes for a Spanish publication sponsored by megastore company K Mart. He also appears in a commercial in Spanish for Old Navy.
On January 8, 2004, rumors surfaced that Mercado would soon be marrying a long-time friend of his.