Gallar scored his first senior goal on 14 April 2010, netting his team's first in a 2–1 home win against Orihuela CF. On 19 June of that year he moved to RCD Mallorca, returning to youth football;[2] he was promoted to the reserves ahead of the 2011–12 season.
Gallar was a key unit in Cultu'spromotion to Segunda División, scoring a career-best 20 goals. On 10 July 2017, he signed a three-year deal with SD Huesca in the second division, for a fee of €400,000.[8]
Gallar made his professional debut on 19 August 2017, starting in a 0–1 loss at CD Numancia.[9] His first goal came on 10 October, in a 1–1 home draw against CF Reus Deportiu; he ended the campaign as a starter, netting eight times as his side achieved a first-ever promotion to La Liga.
Gallar made his debut in the main category of Spanish football on 19 August 2018, starting and scoring a brace in a 2–1 away defeat of SD Eibar.[10] He finished 2018–19 with four goals in 25 appearances (only ten starts, however), as his side was immediately relegated back.
On 21 August 2019, Gallar agreed to a four-year contract with Girona FC in the second level.[11] On 25 September of the following year, he moved to fellow league team FC Cartagena on loan for the 2020–21 season;[12] his loan with the Efesé was renewed for the 2021–22 campaign.
Gallar rescinded with Girona on 14 July 2022,[13] and signed a two-year deal with second division side Málaga CF the following day.[14] On 30 June of the following year, after the club's relegation, he left after activating an exit clause on his contract.[15] On 9 August 2023, he joined Ibiza.[16]