A sermon preached by him in October 1762, produced so favorable an impression on the Empress Catherine II that she summoned him to court to be the religious instructor of the eight-year-old heir apparent, Paul Petrovitch.

Platon remained at the Russian court, winning the admiration of even Voltaire, until the marriage of the heir apparent to Maria Feodorovna, daughter of Duke Eugene of Württemberg, in 1773.

During this time he published, for the use of his royal pupil, his Orthodox Doctrine: or, A short Compend of Christian Theology (Moscow, 1765), in which the influence of Western thought, and even of rationalism, may be distinctly traced.

In 1775 he was enthroned archbishop of Moscow, and throughout the reigns of Catherine II, Paul, and Alexander I diligently promoted the religious, moral, intellectual, and material welfare of his archdiocese, maintaining meanwhile an unceasing literary activity.

He also formalized the arrangement, known as Edinoverie, earlier introduced by Archbishop Nikephoros of Slaviansk, that allowed Old Believer communities to join the established church, while maintaining their traditional form of worship.