Almeida won the Portuguese junior road race and time trial titles in 2016 and spent his under-23 years with Hagens Berman Axeon, taking Liège–Bastogne–Liège Espoirs in 2018 and finishing second overall at the Giro Ciclistico d'Italia the same year. He added the elite Portuguese road and time trial titles in 2019, then signed for Deceuninck–Quick-Step.
Almeida took the maglia rosa on the Etna stage of the 2020 Giro d'Italia, his first Grand Tour, and still had it when the race reached the Stelvio in the final week, eventually finishing fourth. He rode the 2021 Giro in support of Remco Evenepoel and came out of it sixth overall, then won the Tour de Pologne and the Tour de Luxembourg that August.
He moved to UAE Team Emirates for 2022 and sat fourth at the Giro before a positive COVID-19 test ended his race after stage 17. Fifth at that year's Vuelta a España was followed by third at the 2023 Giro, 1'15" behind Primož Roglič, with the white jersey and a stage win at Monte Bondone. It was the first Portuguese Grand Tour podium since Joaquim Agostinho in 1979.
The 2024 Tour de Suisse went to his teammate Adam Yates by 22 seconds, despite Almeida winning the closing time trial. A month later he rode the Tour de France in support of Tadej Pogačar and finished fourth overall. In 2025 he won Itzulia Basque Country, the Tour de Romandie and the Tour de Suisse, taking mountain stages and the uphill time trial that closed the Swiss race.
His 2025 Tour de France ended on stage nine, after a crash on stage seven left him with a broken rib. At the Vuelta a España he led UAE and traded blows with Jonas Vingegaard through the third week, out-sprinting him for the stage win at the summit of the Angliru and finishing second overall at 1'16".









