Studies began at an early age at the Reykjavik School of Singing. Furthering his career, Gardar attended the Hochschule für Darstellende Kunst and Musik in Vienna, had private lessons in New York and Copenhagen and he then took the two year opera course at the Royal Academy of Music in London. His teachers have included David Maxwell Anderson, Stuart Burrows, Paul Farrington, Paul Wynne Griffiths, David Jones, Kiri Te Kanawa, Andre Orlowitz, Robin Stapleton and Michael Rhodes and his versatile voice has enabled him to sing and have success in a wide variety of music - opera, oratorio, lieder, musicals, contemporary music and jazz.

Having been nominated for the Icelandic Music Awards and the Icelandic Performing Arts Awards for his opera roles numerous times as well as being voted sexiest man in the country not once but twice, his singing engagements have taken him to Scandinavia, Europe, USA and Asia and the prestigious venues of the Barbican, Royal Albert Hall and Royal Festival Hall in London and Carnegie Hall in New York which resulted in him becoming the face of and ambassador for the high-end men's clothing line Ermenegildo Zegna. 

He sang at one of the BBC's top featured events; the Proms in the Park in front of 40,000 people, broadcast live to millions of people, and has taken part in a number of their other entertainment programmes, and performed with many prestigious orchestras around the world. He has toured with Katherine Jenkins, Kiri Te Kanawa, Lesley Garrett and Elaine Paige.

Major opera roles have included Ferrando (Cosi fan tutte), Fenton (Falstaff), Alfredo (La Traviata), Rinucchio (Gianna Schicchi), Italian singer (Der Rosenkavalier), Vakula (Cherevichki), Chanfalla (Das Wundertheater), Il duca (Rigoletto), Don Ramiro (La Cenerentola), Nemorino (L'elisir d'amore), Tamino (Die Zauberflöte), Nicias (Thais), Rodolfo (La Boheme) and Don Jose (Carmen).

Cortes has released albums, classical and crossover in both the UK and his native Iceland as well as Germany, Austria, and Switzerland reaching number 1 in the charts in South Africa and Taiwan. He has recorded an album of duets with his father Gardar Cortes Snr entitled 'Island' which received great critical acclaim.

His acting career started at the age of 13 when he won the lead role in a hugely successful European TV series called Nonni and Manni and appearances since have included Curly (Oklahoma), Tony (West Side Story) and Raoul in Phantom of the Opera at Her Majesty's Theatre in the West End of London. Gardar took part in the 25th Anniversary Concert of the Phantom of the Opera at The Royal Albert Hall, a production which was broadcast live to cinemas across the globe and released on DVD. 

Gardar played the Phantom in Andrew Lloyd Webber’s Love Never Dies in Hamburg in 2015-2016 and will play the Phantom in the 30th Anniversary year of Phantom of the Opera in Paris.

Gardar is sponsored by Lexus.