The poll was Tamil Nadu's first assembly election after the demises of the two most prominent Chief Ministers in the state's modern history, J. Jayalalithaa—general secretary of the AIADMK, and M. Karunanidhi—president of the DMK, who died in 2016 and 2018 respectively.

Upon her death, O. Panneerselvam took charge as the Chief Minister, shortly after which Palaniswami was sworn in instead in 2017, who served till the end of the 15th assembly's tenure.

The DMK continued its Secular Progressive Alliance (SPA) with the Indian National Congress, the Communist parties and many others, and named Stalin as its candidate for the Tamil Nadu Chief Minister's Office.

The votes were counted on 2 May 2021; the SPA amassed 159 seats, with the DMK alone winning in 133 constituencies, securing an absolute majority for the first time in 25 years.

Following Jayalalithaa's demise from cardiac arrest on 5 December 2016, O. Panneerselvam of the AIADMK became the Chief Minister of Tamil Nadu for the third time.

Later in the evening, Sasikala met the Governor and laid claims to the Chief Ministership, by submitting the list of AIADMK legislators who back her.

On 17 April 2017, Delhi Police registered a case against Dhinakaran for allegedly attempting to bribe the Election Commission into giving the AIADMK's significant Twin Leaves symbol to his faction.

This marked the first time the BJP began to play an influential role in the Tamil Nadu politics, acting as the mediator that united the two factions.

[15][16] On 22 August 2017, 18 MLAs of the AIADMK pledged allegiance to Dhinakaran and submitted letters to the Governor, expressing lack of confidence in Palaniswami and withdrawing their support to the Palaniswami-led government.

The Speaker of the fifteenth Tamil Nadu Legislative Assembly, P. Dhanapal, also disqualified those MLAs from their offices, citing the Constitution Act of 1985, which prevents the instability caused by democratically elected representatives in India's legislatures shifting allegiance from the parties they supported at the time of election, or disobeying their parties' decisions at critical times, by rendering their seats vacant.

He became the first independent candidate in Tamil Nadu history to win a bypoll, claiming 50.32% of the total votes, defeating the ruling AIADMK and the opposition DMK.

[19][20] In March 2018, Dinakaran formed the new party Amma Makkal Munnettra Kazagam (AMMK), with the goal of obtaining control of the AIADMK.

[28] The AIADMK & BJP also fulfilled the demand of grouping 7 castes under Devendrakula Velalar an agricultural community found in Tamil Nadu.

[29] Recent events such as the Thoothukudi protest in 2018 against the district's Sterlite Copper plant and the Kattupalli fishermen's agitation against the expansion of Adani port have also made environmental concerns, especially climate change, a topic of debate in the elections.

[31] Election Manifesto plays a key role in determining the voting behaviour of the voters in the Tamil Nadu Electoral Politics.

[33][34] Global Shapers Chennai, a non-partisan group powered by the World Economic Forum has released the TN Election Promises 2021 platform.

[35] The platform provides the voters with data and insights on the promises made by different parties, constituency-wise candidate background details (assets, education, criminal cases, etc.

BJP politician and the Chief Minister of Uttar Pradesh, Yogi Adityanath, addressed a public rally in Coimbatore in presence of Annamalai K to support Vanathi Srinivasan on March 31, 2021.

The Indian National Congress candidate for Srivilliputhur Assembly constituency, P. S. W. Madhava Rao, died on 11 April 2021 after testing positive for COVID-19.

The repoll follows the suspension of three Greater Chennai Corporation officials for transporting two EVMs and one VVPAT machine of booth number 92 on a two-wheeler in the Velachery-Tharamani road.

After spending a decade as the opposition party, the DMK won Tamil Nadu from the AIADMK, which reigned the state for two consecutive terms (2011-2021).

[88] During the early hours of the same day, DMK president Stalin paid respects at the memorial of his father and five-time Chief Minister, M. Karunanidhi.

Speaking to the journalists gathered there, Stalin stated that he will be sworn in as the Chief Minister in a simplistic ceremony that may be held at the Raj Bhavan, the Governor's residence.

[89] After the resignation of Palanisami's administration, officials of the Public Works Department began resetting the Tamil Nadu Secretariat to prepare the campus for the new government under Stalin.

[89] Narendra Modi, the Prime Minister of India, tweeted that he will work with Stalin to enhance the nation's progress, fulfill the regional interests of Tamil Nadu, and fight the COVID-19 pandemic.

[91] On 10 May 2021, the newly elected AIADMK MLAs convened to choose the new Leader of the Opposition, an important post equivalent to a cabinet minister.

Supporters of Palaniswami believed that he should be the Leader of the Opposition due to the party's good performance in the election in western Tamil Nadu, the region he hails from; whereas, Panneerselvam's supporters felt that the party fared poorly in other regions of the state due to Palaniswami's wrong policies during his Chief Ministerial tenure.

[93] After MNM performed unfavorably in its first-ever election, many officials and candidates resigned from the party, such as its vice president Dr. Mahendran, Muruganandam, C K Kumaravel.

Mahendran said that "the attitude of Kamal Haasan towards the growth of the party has not been changed even after facing huge loss in the Tamil Nadu assembly election".

In the meeting, the 133 MLAs formally extended their support to Stalin's appointment as the DMK's head at the Tamil Nadu Legislative Assembly, making him the Chief-Minister-elect.