Petar Atsev was a representative of the Prilep revolutionary region at the Congress of Smilevo, where he was one of the principal antagonists to the idea of organizing and carrying out the Ilinden-Preobrazhenie Uprising.

Petar Atsev, together with Georgi Pophristov and Lazar Poptraykov, was chosen a reserve member of the Uprising Staff, which was led by Dame Gruev, Atanas Lozanchev and Boris Sarafov.

[8] In 1905, Trayko Kralya, Petar Atsev and Gyore Spirkov, nicknamed Lenishtanets, and Krastyo Germov had a meeting with Gligor Sokolovich, who used false documents to persuade them to let him enter Macedonia.

[9] At the Congress of Kyustendil in 1906, Petar Atsev was chosen an additional member of the Central Committee of the IMARO, together with Petko Penchev, Pavel Hristov, Efrem Chuchkov, Argir Manasiev and Stamat Ikonomov.

In 1907, he participated in the Battle of "Nozhot" (the Knife), together with the voyvodas Tane Nikolov, Ivan Naumov, Mihail Chakov, Hristo Tsvetkov and Mircho Naydov.