In 1379, the Grand Prince of Moscow, Dmitry sent him to Constantinople with his nominee for the metropolitanate, the Archimandrite Mitya [ru], where the latter was to be consecrated by the Ecumenical Patriarch.

Mitya, sometimes referred to as Mikhail, was a secular (non-monastic) priest and Namestnik (vicar) of the late Metropolitan Alexius of Kiev (in office: 1354 to 1378) as well as the Pechatnik ( carrier of the seal) of the Grand Prince.

In fact, the Grand Prince sent his confessor, Hegumen Fedor of the Simonovskii Monastery, to Kiev to bring Cyprian to Moscow (he arrived in May of that year).

The Patriarch convened a council to decide the matter, but procrastinated for three years, leading Dmitry Donskoy to finally dismiss the Greek metropolitans in Moscow and to 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 11 September 1389 and was buried in the Church of John the Forerunner.