Radoslav made his first team debut in a 3–0 league win over Montana on 27 May 2011, coming on as a substitute for Darko Tasevski.

[1] Tsonev scored his first goal for Levski in the Eternal derby of Bulgarian football against CSKA Sofia on 21 April 2014.

During the first of these two seasons, the two brothers were the leaders of Levski, gaining somewhat of a cult status among fans due to their loyalty to the club in times of financial hardship.

Following the appointment of Stanimir Stoilov in September 2021, Tsonev progressively lost his place in the starting eleven.

He made his debut for the Bulgaria national football team on 12 October 2021 in a World Cup qualifier against the Northern Ireland.