A former member of Battalion 49 in Astoria, Queens, Mercado, 63, on Thursday received the $5 million top prize from a Cash X100 scratch-off lottery ticket.
"I'm now a part of the New York lottery family," Mercado said at news conference.
Mercado's career ended after 9/11 because of health problems that continue to affect him, he said. He now devotes his time to being a father to his four children, including a 10-year-old daughter.
He retired in 2004 after a doctor at the fire department told him he had too much lung damage to continue to work.
Mercado said he has two daughters and two sons. He spends most of his days with his youngest daughter; he plans to buy her 10 "American Girl" dolls.
"Everything is beautiful now," he said.
Mercado is a regular New York lottery player. In May, he decided to try the Cash X100 game after a friend told him it could bring him luck.
Mercado said he bought one ticket and lost.
The next ticket in the batch was number 25, the inverse of his birth year. He decided to try his luck. He scratched on the second ticket to see a "500," and then gradually more commas until he realized that the number was "5,000,000."
"I said, 'Holy mackerel, that looks like $5 million," he recalled.
He will receive a check totaling $3,309,000 after withholdings.
Mercado said the first thing he thought after discovering he had won was "freedom."
"I will certainly help out my family and this year's Christmas presents will be a little bigger than last year's," he said. "But I'm really excited to buy a summer house at Disney. We go as a family every year and it will be nice not to have to rent anymore."
Mercado also hopes to take his family on a Caribbean cruise.
"I'm just pacing myself," he said. "I'm still in shock."