Known as the "Sol-Train", he had an impressive PBA rookie season and eventually became a reliable point guard for most of the teams he played for.

[1] However, he was immediately traded to the Rain or Shine Elasto Painters, together with Eddie Laure for Joe Devance and the 2009 and 2010 second round picks of Alaska.

If not for a hamstring injury that sidelined him in a couple of games into their semifinal series against the Barangay Ginebra Kings,[3] Rain or Shine would probably have gone farther in the Fiesta Conference.

A member of the All-Rookie Team,[4] Mercado finished second to teammate Gabe Norwood for Rookie of the Year honors.

[11] Before the start of the 2013 PBA Commissioner's Cup, he along with Kelly Nabong, Jaypee Belencion and Yousif Aljamal were traded to GlobalPort Batang Pier for Rey Guevarra, Vic Manuel, Josh Vanlandingham and a 2015 first round pick.

[12] This made him the first-ever player in PBA history to be traded or moved to another team after leading the league in scoring and assists the previous conference.

[15] During the 2013 Governors' Cup, tension arose between him and his coach Junel Baculi over an uncalled timeout in a loss to the Barako Bull Energy.

[20] Before the start of the 2014 PBA Commissioner's Cup, Mercado was traded to San Miguel in exchange for Alex Cabagnot.

[25] On January 8, 2015, Mercado was traded again by GlobalPort, this time to Barako Bull which gave up Denok Miranda and a 2016 second round pick.

[26] To begin the 2015 Commissioner's Cup, he had 20 points, three assists, and a steal in a winning debut over the Blackwater Elite.

[27] On May 4, 2015, before the start of 2015 PBA Governors' Cup Mercado was traded to Barangay Ginebra in exchange of Joseph Yeo.

[36] He then started at small forward for the injured Chris Ellis, and contributed 19 points and four assists in a win over Meralco.

[39] In the semis, they went up against sister team San Miguel, where in Game 1, he had 19 points, five assists, three boards, and one steal in 36 minutes off the bench as Ginebra went up 1–0.

[42] In Game 2, he defended Meralco's import Allen Durham, and scored the game-winning putback, tying the series.

[57] In the Philippine Cup, Mercado helped Ginebra clinch a spot in the semifinals by putting up solid numbers against Rain or Shine.

[65] On June 18, 2019, Mercado, along with Jervy Cruz and Kevin Ferrer, was traded back to the Batang Pier for Stanley Pringle.

In his first game back, he started and added 14 markers, five caroms, five dimes, a steal, and a block in a win over Blackwater.

[71] On January 20, 2020, Mercado was traded to the Phoenix Pulse Fuel Masters for LA Revilla and Rey Guevarra.

[79] [80] Mercado is half-Filipino and half-Puerto Rican, with his mother Rosalie from Pampanga and his father Aaron from Puerto Rico.

[82] However, on October 20, 2016, a day after Ginebra won their first title after 8 years, Laurel announced through her Instagram account that they have ended their relationship.

[83] On September 29, 2021, Mercado and beauty queen Sandra Lemonon announced on their respective Instagram accounts that they are in a relationship.