His career as a television astrologer was launched when his longtime friend, famed Puerto Rican television producer
Elin Ortiz, asked him to fill in for an invited guest on a popular midday talk show in Puerto Rico who failed to show up at the last minute. Mercado's discussion on his knowledge of astrology was a hit among audiences on the island that he was invited back weekly to the show, and eventually given his own spin-off show.