He is best known for his role of Andrés "Berlin" de Fonollosa in the Spanish heist series Money Heist (La casa de papel) and its spin-off Berlin, and for the role of Diego Murquía in the historical drama series Gran Hotel.

[1][2] He studied at Royal School of Dramatic Arts (RESAD) in Madrid, graduating in 1992, and at Teatro de la Danza (Theatre of Dance).

[3] Alonso is known for his performances on television in Rías Baixas (2003–2005), Maridos e mulleres (2006–2008), Padre Casares (2008–2015), and Gondar (2009) at a local level in Galicia and nationally for playing characters such as Diego Murquía / Adrián Vera Celande in historical drama Gran Hotel.

He co-starred in Diablo Guardián, Amazon Prime Video’s first drama series in Latin America, which was released in May, 2018.

In 2019, Alonso played the leading role in the mystery thriller The Silence of the Marsh.