Sir Thyagaraja Sadasiva Iyer (23 June 1861 – 1 December 1927) was an Indian judge and theosophist who served as the Chief Justice of Travancore from 1905 to 1910.

Sadasiva was born in a Tamil Brahmin family in Kumbakonam[1] on 23 June 1861 to Mangudi Thyagaraja Iyer,[2] who was a daayadhi (cousin by paternal lineage) to Nobel Laureate C. V. Raman.

[3] Sadasiva started his judicial career as an apprentice to Raja T. Rama Rao before enrolling as a vakil in the Madras High Court.

[2] In 1921, he was appointed President of the Hindu Religious and Charitable Endowments Department (HR & CE), newly established by the Justice Party government of the Raja of Panagal.

Sadasiva was an active member of the Theosophical Society[7] presiding over several meetings and serving as the General Secretary of its India Section from 1924-1925.