Méndez joined the Independiente del Valle academy in 2011. By 2014 he had been promoted to the club's B team and made his first-team debut on 7 March 2015 in a victory over L.D.U. Loja in the Serie A Primera Etapa. After two substitute appearances, Méndez was loaned to Cultural Leonesa in Spain, making one substitute appearance for the club on 29 November 2015. Upon his return to the club, Méndez had to wait until gameweek 15 of the 2016 season to play his next game, appearing as a substitute in a defeat to Fuerza Amarilla on 13 May 2016. He followed that up by playing the full 90 minutes in six of the final ten games of the Serie A Primera Etapa and a further 12 appearances in the Segunda Etapa as he cemented himself as a first-team regular.
On 7 November 2021, Méndez scored his first goal for the club on his 65th appearance. The goal, a spectacular knuckling 20-yard strike, was the opener in an eventual 2–0 win away at CF Montréal. It was the final match of the regular season in which Orlando entered knowing a draw would guarantee qualification to the 2021 MLS Cup Playoffs.[6]
Los Angeles FC
On 19 July 2022, Méndez was acquired by Los Angeles FC via trade in exchange for $300,000 of General Allocation Money (GAM). Orlando could receive an additional $450,000 in GAM if certain contract conditions are met and also retained an undisclosed percentage of any future transfer fee.[7]
On 9 January 2023, Méndez joined Brazilian club São Paulo on a free transfer, signing a three-year contract.[11] Rarely used in his first season, he was loaned to Spanish Segunda División side Elche on 1 February 2024.[12]
In October 2018, Méndez was called up to the senior Ecuador national team by manager Hernán Darío Gómez for the first time.[14] He made his debut on 11 September 2018, playing 73 minutes in a 2–0 friendly victory over Guatemala at Toyota Park, Bridgeview, Illinois.[15][16] In May 2019, he was called into the squad for the 2019 Copa América, his first senior international tournament.[17] After sitting out the first group game, Méndez started against Chile and drew a foul from goalkeeper Gabriel Arias to win a penalty, Ecuador's only goal of a 2–1 defeat.[18] He started the following game, a 1–1 draw with Japan. Ecuador were eliminated after finishing bottom of Group C with one point.