Varela joined Boca Juniors in 2012 from Barcelona Luján; a subsidiary of Barcelona, who later became known as Barcelona Juniors following a partnership with Boca.[2] After training with Boca's senior side during 2019, a year that also saw him sign his first professional contract, Varela made the breakthrough into Miguel Ángel Russo's first-team in 2020.[4][5][6] He was an unused substitute seven times in all competitions between September and December, including for the first time on 17 September for a Copa Libertadores win over Libertad.[3] Varela's senior debut came on 20 December in a Copa de la Liga Profesional game with Independiente.[3][7][8][9]
Porto
On 16 August 2023, Primeira Liga club Porto announced the signing of Varela on a five-year contract,[10] for a reported fee of €8 million + €3 million in performance-related add-ons.[11] He made his debut on 3 September, coming off the bench to replace Stephen Eustáquio at half-time in a 1–1 league draw at home against Arouca.[12] Twelve days later, Varela made his first start for the Dragons, away at Estrela da Amadora, where he made a last-minute goal-line clearance to guarantee a 1–0 Porto win.[13] On 20 January 2024, he scored his first goal for Porto, in a 5–0 league victory at home to Moreirense.[14]