In 1872 he was invited by the Bulgarian Orthodox Exarch in Constantinople, and was ordained in the Episcopal rank in July 1873 with the title Smolenski.

At this time there was widespread rumor that the Bulgarian Church was preparing an agreement with the Greek Patriarchate, whereby the Exarchate should abandon its positions in Macedonia.

The rumor was based on the real position of the Russian ambassador in Constantinople Count Nicholas Ignatiev, who was restrained on the issue of extension of the Bulgarian Exarchate's influence in Macedonia.

As a result, three of them (Thessalonika, Voden and Kukush) required from the Exarchate a new independent diocese to be set up and Nil to become its bishop.

After the death of Bishop Rafael Popov in September, 1876 the Holy See Nil was appointed as a spiritual head of the Uniate Bulgarians.

In the spring of 1895, after long hesitation, Archbishop Nil appealed to the Bulgarian Holy Synod to be re-admitted to the Orthodox Church.