The election was held to fill the vacancy in the upper house from Andhra Pradesh after the death of N Janardhan Reddy, an official release said.
The announcement of Sitharaman's election was made as today is the last date for withdrawal of nominations.
Sitharaman, Union Minister for Commerce and Industry (Independent Charge) was the only candidate to contest in the poll.
The ruling TDP has backed the candidature of Sitharaman, who is married into a coastal Andhra family.