Jagga Reddy's candidature was announced Wednesday soon after he quit the Congress and joined BJP.
A former legislator of Congress party, Jagga Reddy sprang a surprise by joining the BJP as only recently he was appointed president of Medak district of the Congress.
BJP Telangana president G. Kishan Reddy announced party's candidate at a press conference in the presence of Jagga Reddy at the party office.
Meanwhile, the Congress party has named former minister Sunita Lakshma Reddy as its candidate.
Kotha Prabhakar Reddy Wednesday filed nomination as Telangana Rashtra Samithi (TRS) candidate.
Wednesday is the last day for filing of nominations for Sep 13 by-election, caused by the resignation of TRS president and Telangana Chief Minister K. Chandrasekhar Rao.
Rao was elected both from Medak Lok Sabha and Gajwel assembly constituencies in the elections held in April.