Nicknamed El Chiqui (meaning Short or Small), due his height when he was at youth levels, he turned professional with Cartaginés before moving to the north of Norway. Making an impressive rookie season scoring 21 goals in only 30 games.
He joined Bodø/Glimt with his compatriot Roy Miller, who was also a teammate in Cartaginés, in 2005. At this point Bodø/Glimt was part of the Norwegian top division (Tippeligaen), but got relegated the same year. The team therefore played in Adeccoligaen in 2006 where Brenes was top scorer with 13 goals, 6 of them off headers. In 2007, the team gained promotion to Tippeligaen after winning at home and away against Odd Grenland from Tippeligaen. Bodø/Glimt had a big positive surprise the following season in Tippeligaen, ending on a fourth place.
Brenes was loaned at the middle of the season to Adeccoligaen team Kongsvinger to help them remain the at the division, his compatriot Roy Miller, in the meantime, was sold to Rosenborg of Trondheim. In 2009, Brenes signed a full-time contract and helped Kongsvinger win promotion to Tippeligaen. But after the season ended, Brenes came to an agreement with the club to terminate his contract, because he wanted to move home to Costa Rica with his family.
Randall Brenes back for the tournament in Summer 2010 and Winter tournament in the same year shared the scoring with Éver Alfaro and helping the team reach the semifinals. Brenes spent the 2010 and 2011 seasons with Cartaginés and winning two scoring titles, one in the tournament in 2010 winter and the other in the 2011 winter tournament and being the best player declared by the Primera División de Costa Rica in the winter 2011 and carrying to Cartaginés to fourth in the table, scoring in four minutes in the first half on the first semifinal but losing against the Herediano 3–1 on aggregate.
On 9 February 2012 Brenes signed a 2-year long contract with Khazar Lankaran. On 20 February 2012, made his debut in the season in a 2–1 defeat against Gabala and entering the 35th minute change by António Semedo and receiving a yellow card. On 7 March 2012, plays its first game start against Turan, playing 90 minutes. 14 March 2012, plays its first match in the quarterfinals of the Azerbaijan Cup in the 3–2 defeat against Baku Inter, scoring his first goal for the club and the second goal of the team at minute 57 and playing 90 minutes. On 28 March 2012, played 90 minutes in the second leg of the Azerbaijan Cup against Inter Baku scoring his second goal, a 1–1 draw at 76 minutes. On 11 May 2012, income also a starter in the 4–1 victory against Qarabağ, scoring the second goal at 22 minutes and out of change by Stevan Bates at minute 70. In the 2012–13 season, Brenes played four games for the club, all the Europe League. On 5 July 2012, playing 90 minutes against Nõmme Kalju and received a yellow card 53 minutes. On 10 July 2012, plays the second leg entering the 84th minute change by Sadio Tounkara. Then play in both games as a substitute, for the second round of Europa League against Lech Poznan. On 31 July 2012, Brenes signed his termination of contract due to breaches of the team with the player.
On 7 August 2012, Brenes sign a 1-year long contract with Cartaginés.
On 4 August 2014, Brenes signed a loan deal with Sandnes Ulf.
He made his debut for the Ticos in 2005 as a substitute against Cuba at the CONCACAF Gold Cup Finals, immediately making an impact by scoring 2 goals. In January 2011, he returned to play in the selection of Ricardo La Volpe in Panama 2011 Copa Centroamericana, playing 5 games. On 26 March 2011, Randall Brenes played on the first game of the Estadio Nacional de Costa Rica against China and be in the history scoring the second goal of Costa Rica. In June 2011, played in two 2011 CONCACAF Gold Cup matches against Cuba and El Salvador scoring in stoppage time. In July, Brenes played two match against Colombia and Argentina in the 2011 Copa América.
As of January 2014, he has earned a total of 36 caps, scoring 8 goals and has represented his country in 8 FIFA World Cup qualification matches.
On 20 June 2014, Brenes make his debut at the second round of group stage matches in the 2014 FIFA World Cup, entering replacing of Bryan Ruiz at 81 minutes, playing 9 minutes plus 4 minutes replenishment at the Itaipava Arena Pernambuco, taking a chance on goal but his shot went wide. In the third round of group stage matches, against England in the Estádio Mineirão, entry from the beginning and came out in the 59th minute by Christian Bolaños. On 29 June 2014, plays his third game in the cup against Greece at the Itaipava Arena Pernambuco for the round of 16, entering as a substitute in the 83rd minute, replacing of Christian Bolaños, playing all the extra time and make history with the Ticos, winning the game 5-3 on penalties shoot-out after the 1-1 on the 120th minutes and advance to the Quarter-finals.As of 11 September 2013
As of 16 November 2014
UNCAF Nations Cup:
Player of the season at Cartaginés: 2010 and 2011