Shortly thereafter, Maharaja Sayajirao Gaekwad III appointed him as his personal secretary, and subsequently as a tutor of the princes.

He often accompanied the Maharaja during the latter's trips to the UK, US, and Europe; this helped Sardesai to broaden his outlook of history.

In accord with a suggestion from Jadunath Sarkar, the government of Bombay asked Sardesai to take up the work of editing and publishing the Peshwa daftar.

Subsequently, he published 45 volumes of the Peshwa daftar, 7,801 pages long in total and covering 8,650 documents.

Later, jointly with Sarkar, Sardesai edited and published the Poona Residency Correspondence consisting of 7,193 pages and covering 4,159 letters.