Alonso was born in Spain in 2006. He first came to prominence in 2020 by winning the European Talent Cup, then followed that title with the 2021 Red Bull MotoGP Rookies Cup, clinching the latter championship by finishing third in the first race of the Aragón round on 11 September 2021. These back-to-back junior titles marked him as one of the highest-potential prospects in the Grand Prix motorcycle racing pipeline.
Alonso was signed by the GasGas Aspar Team and made his Moto3 World Championship debut at the 2021 Emilia Romagna Grand Prix as a replacement for Sergio García, who had been injured in the previous round. In 2022 he made a second start as a wildcard at the Portuguese round. He graduated to a full-season role for the 2023 Moto3 World Championship, gaining consistent experience across the entire calendar.
The 2024 season proved exceptional. Alonso dominated Moto3 to an unprecedented degree, winning 14 races from the season — including seven consecutive victories spanning the Emilia-Romagna, Mandalika, Motegi, Philip Island, Buriram, Sepang, and Barcelona rounds — and accumulating 421 championship points. He was crowned champion at the Japanese Grand Prix. His final winning margin of 165 points over the runner-up set the record for the largest title-winning margin in Moto3 history. His 14 wins in a single season also surpassed the all-time record for most victories in any class in a single Grand Prix motorcycle racing season.
Upon completing this campaign, Alonso held multiple Moto3 records: most wins in the category's history (18), most wins in a single season (14), most consecutive wins (7), most points in a single season (421), and highest single-season win percentage (42.86%). He became the first rider to complete the full Aspar Team training ladder, from the Spanish domestic championship through to Moto2.
After his dominant Moto3 title, Alonso stepped up to Moto2 with the CFMoto Aspar Team for 2025, partnering Daniel Holgado. The pairing brought together two of the most decorated recent graduates of the Aspar Academy. He continued with the team into the 2026 season.
Alonso's 2024 Moto3 campaign stands among the most dominant individual seasons in the history of Grand Prix motorcycle racing. His record haul across multiple statistical categories redefined expectations for a single-season performance at the entry level of the World Championship, and his dual national identity as a Colombian-Spanish racer brought broader visibility to Colombian motorsport on the international stage.