On 9 September 1944, he became a member of the Committee of the Fatherland Front at Sofia University and the Medical Faculty.

In 1948, his parliamentary immunity was revoked and Dertliev was sentenced to ten years in prison "for counter-revolutionary activities".

He was imprisoned in Venchan and Belene (2-fold), Pleven Prison, criminal division and in jail for repeat offenders in Pazardzhik.

After the political changes of 1989, Dertliev, together with Atanas Moskov, initiated the reconstruction of the Party of Bulgarian Social Democrats (BSDP).

Although Dertliev signed the new Constitution he disagreed with the position of the 39 MPs and left the parliament.

In 1994 he was the first chairman of the rotation of Political Union Democratic Alternative for the Republic (DAR).