Born in Santa Cruz de Tenerife, Canary Islands to a Guinean father and a Spanish mother, Thierno was a CD Tenerife youth graduate, and made his senior debut with the C-team in the 2018–19 season, in the regional leagues.
[1] He made his first team debut on 4 September, coming on as a late substitute for Álex Corredera in a 2–0 Segunda División home win over SD Ponferradina.
[2][3] On 1 September 2022, Thierno was loaned to Primera Federación side SD Logroñés for the season.
[4] On 19 March 2022, Thierno was called up to the Guinea national team by manager Kaba Diawara for friendlies against South Africa and Zambia.
[5] He made his full international debut six days later, starting in a 0–0 draw with the former at the Guldensporen Stadion in Kortrijk, Belgium.