He was hegumen of the Goritskii Monastery in Pereiaslavl-Zalevskii when Grand PrinceDmitry Donskoy sent him to Constantinople with his nominee for the metropolitanate, Mitya, where the latter was to be consecrated by the Ecumenical Patriarch. Mitya, sometimes referred to as Mikhail, was a secular priest and Namestnik of the late Metropolitan Alexius as well as the Pechatnik of the Grand Prince. Mitya, however, died within sight of Constantinople and was buried at Galata, and Pimen was consecrated in his place, although this was done without the knowledge of the Grand Prince and the Patriarch was said to have been tricked, as Pimen had apparently used forged grand princely letters to get Patriarch Nilus of Constantinople to consecrate him. Donskoy was angry upon hearing the news of Pimen's consecration and swore not to accept Pimen upon his return. Thus Pimen's metropolitanate was contested from the start, and he accomplished little as a result. While Cyprian had been the rightful metropolitan – he had been named Metropolitan of Lithuania and Western Rus' and was to succeed to the Metropolitanate of Kiev and All Rus' upon the death of Metropolitan Alexius in 1378, the grand prince only accepted him in March 1381 because of his anger at Pimen's consecration. In fact, Donskoy sent his confessor, Hegumen Fedor of the Simonovskii Monastery, to Kiev to bring Cyprian to Moscow. When Pimen arrived back in Russia, he was arrested by the grand prince and sent to Chukholm in the Kostroma district. Upon hearing the news, Patriarch Nilus excommunicated Donskoy and imposed an interdict, whereupon Donskoy deposed Cyprian, whom he blamed for the matter. Cyprian was banished from Moscow in October 1382 and Pimen allowed to come to Moscow and take up his duties as metropolitan; Donskoy wanted to avoid excommunication and interdiction – his personal feelings, however, had not changed. Pimen was himself deposed in 1384; the grand prince, still angry at the illegitimate natuer of Pimen's election, filed charges and sent Pimen to the Patriarch in June 1384 to answer the charges. Nilus, claiming ignorance of Pimen's conspiracy to become metropolitan, ordered two metropolitans be sent to Moscow to investigate. Dionysius of Suzdal, who had opposed Pimen in 1382, was sent as well, but traveled instead to Kiev, when he tried to negotiate with Cyprian, the rightful metropolitan. While Pimen was deposed that winter and Dionysius apparently was to be consecrated in his place, in fact, Dionysius was arrested in Kiev at Cyprian's instigation and died in confinement there in October 1385. In May 1385, Pimen went to Constantinople to plead his case, but Cyprian arrived there shortly thereafter to argue that he was rightful metropolitan. The Patriarch convened a council to decide the matter, but procrastinated for three years, leading Donskoy to finally dismiss the Greek metropolitans in Moscow and send his confessor, Fedor, to plead for Pimen's removal. Pimen had returned to Moscow in 1388, but was never reinstated and left again for the Byzantine Empire in April 1389 to appeal, yet again, to the Patriarch of Constantinople; he remained in Chalcedon, where he died on September 11, 1389 and was buried in the Church of John the Forerunner. Donskoy had died the previous May, and his son, Vasilii, finally accepted Cyprian as metropolitan in Moscow.
