The 2012 Andhra Pradesh Legislative Assembly by-election was held from March to June 2012 in three phases to fill vacancies to the 25 seats in the Andhra Pradesh Legislative Assembly, following the death, resignation and disqualification of the incumbent members.
Following the 2009 Andhra Pradesh Legislative Assembly election, Y. S. Rajasekhara Reddy was sworn in as Chief Minister of Andhra Pradesh but died shortly thereafter in a helicopter crash. His death, along with the intensifying Telangana movement, contributed to a period of political instability in the state. His son, Y. S. Jagan Mohan Reddy later fell out with the Indian National Congress (INC) and formed the YSR Congress Party (YSRCP). Many MLAs in the Andhra region left the INC to join YSRCP, while in the Telangana region, several MLAs joined the Telangana Rashtra Samithi in demand for a separate state. These mass defections led to disqualifications, leaving assembly seats vacant and necessitating by-elections, which were held on 10 March 2012 for 1 seat, on 18 March 2012 for 6 seats and on 12 June 2012 for 18 seats.
The enforcement authorities seized approximately Rs. 32 crores in cash and gold valued around Rs. 9 crore, taking the total to Rs. 41 crore. Nearly 1.74 lakh litres of liquor were confiscated during the campaign period. The reported total exceeded the amount seized during the 2009 Andhra Pradesh Legislative Assembly election.
On 27 May 2012, the Central Bureau of Investigation (CBI) arrested Y. S. Jagan Mohan Reddy in connection with alleged disproportionate assets and corruption charges. The CBI alleged that Jagan had received investments from various companies in return for granting undue favours during the tenure of his father, Y. S. Rajashekhara Reddy as Chief Minister of the state from 2004 to 2009. Following his arrest, Jagan was remanded to judicial custody and lodged in Chanchalguda Central Jail, Hyderabad. His bail petitions were rejected multiple times.
With Jagan in judicial custody, the party's campaign was led by his mother Y. S. Vijayamma and his sister Y. S. Sharmila. Sharmila addressed multiple public meetings across constituencies, appealing to voters on grounds of perceived injustice and continuity of her father's welfare activities.
Public sentiment during the by-election varied regionally, with voters in the Telangana region focused on the demand for a separate state, while in the Andhra region, the arrest of Y. S. Jagan Mohan Reddy was an electoral factor.
The result for the first and second phase of the by-election was declared on 21 March 2012. For the first time, 3G technology was used to upload polling and counting data to the internet more quickly, with the counting process recorded using the web cameras. The TRS won 4 seats, while the Bharatiya Janata Party, the YSRCP and an independent candidate won one seat each.
The third phase result was declared on 15 June 2012, the YSRCP emerged as the largest winner, winning 15 of the 18 contested seats. The INC won 2 seats, increasing its majority to 154 seats in the 294 member Andhra Pradesh Legislative Assembly. The TRS won one seat and the Telugu Desam Party drew blank. Notably, all the incumbent members who had resigned and re-contested were re-elected in both phases.
Following the declaration of the results, Y. S. Sharmila stated that her brother Y. S. Jagan Mohan Reddy, who was then in judicial custody in connection with corruption charges, should become the Chief Minister in 2014. Chief Minister N. Kiran Kumar Reddy subsequently held meetings with party leaders and legislators to review the results.
The Hindu read this as possibly predictive of the 2014 general election. It also said that while the YSRCP was the favourite, there was a keen eye on who would finish second between the INC and the TDP. Rediff headlined the result as the "fledgling YSR Congress party...has swept the by-elections in Andhra Pradesh, denting the last bastion of Congress in south." It also pointed out that the loss of Tirupati was significant as it was the home district of the INC Chief Minister N. Kiran Kumar Reddy and had previously been won by Chiranjeevi before his resignation to seek a Rajya Sabha seat. The Economic Times referred to the YSRCP's successful result as "riding on the sympathy wave in the wake of its leader Y.S. Jaganmohan Reddy's arrest", and the Hindustan Times had a similar assessment.