Four parties contested the by-election, as opposed to the 19 that contested the 2002 general election. Similar to general elections, the by-election elected three MPs through a party-list proportional representation system using the D'Hondt method. The parties contesting the election were the Justice and Development Party (AKP), the Republican People's Party (CHP), the Workers' Party (İP) and the Communist Party of Turkey (TKP). The AKP won all three seats up for election with 84.82% of the votes, gaining the two other seats that had been won by the CHP and an independent candidate in November 2002. The CHP came second with 13.79% of the vote and lost their seat despite increasing their vote share since November.
The Province of Siirt is a province in the south-east Anatolia region of Turkey with a predominantly Kurdish population. With an electorate in 2003 of approximately 119,198, it elects three of the 550 MPs to the Grand National Assembly. In the 2002 general election, the province was won by the Kurdish nationalistDemocratic People's Party (DHP), which gained 32.17% of the votes. Since the party polled below 10% nationally, it was unable to win any parliamentary seats. According to the Turkish electoral system, the DHP's votes were allocated to the winning party of the election, namely the Justice and Development Party (AKP), which had come second with 17.56% of the vote. Turkish businessman Fadıl Akgündüz was elected as an independent with 13.65% of the votes, coming third. The CHP came fifth with 8.92% of the vote, but won the province's final MP since it was the only other political party apart from the AKP to poll above 10% nationwide.
In the 2002 general election, Recep Tayyip Erdoğan's AKP won 363 seats in Parliament and formed the first single-party government since 1987. While serving as Mayor of Istanbul in 1998, he had been convicted of reciting a poem which incited religious intolerance in Siirt and sentenced to 10 months in prison. After serving four months, Erdoğan founded the AKP in 2001 as a moderately Islamist political party, capitalising on voter dissatisfaction with the existing political parties and their poor economic records. His imprisonment forced him to give up the mayoralty and resulted in a political ban. Despite being the AKP leader, Erdoğan was unable to seek parliamentary election in 2002 and thus the party's co-founder Abdullah Gül became Prime Minister instead. With the help of the opposition CHP, Gül pushed forward constitutional reforms which nullified Erdoğan's political ban and allowed him to run for office.
The local electoral authorities investigated irregularities in the district of Pervari in south-eastern Siirt. The alleged irregularities were the fact that three ballot boxes in a village named Doğan Köy were broken and thus could not be voted in, meaning 706 voters boycotted the election in protest. The number was significant since had the AKP won 122 more votes, it would have gained two MPs rather than just one in 2002.
On 2 December 2002, the Supreme Electoral Council of Turkey declared the general election in Siirt null and void and ordered a repeat scheduled for March, citing the broken ballot boxes as having an influence on the results and the subsequent MP distribution. Since Recep Tayyip Erdoğan's political ban had been annulled, the AKP's first candidate Mervan Gül voluntarily stepped aside so that Erdoğan could take his place. Gül subsequently became the AKP Mayor of Siirt in the 2004 local elections.
The Workers' Party legally contested Erdoğan's candidacy, claiming that the by-elections were a repeat of the general elections and thus the party candidate lists could not be changed. This complaint was rejected by the Supreme Electoral Council. The council further ruled that independent candidates which did not run in 2002 would not be able to declare their candidacy in the by-election.
Critics of the AKP have often accused the government of deliberately forcing the Supreme Electoral Council to call a by-election so that Erdoğan could become Prime Minister. Despite allegations that ballot boxes were broken, the residents of Doğan Köy refused to vote until their village received the support it needed during periods of heavy snow, putting the reasons for their boycott in question. The AKP government began a heavy snow clearing operation in the village before the by-election. The initial complaints that ballot boxes had been broken had been made by the AKP. Controversies regarding the exact reasons why the AKP's initial candidate Mervan Gül stepped down, as well as the Supreme Electoral Court's decision to ban Fadıl Akgündüz from running again as an independent due to an arrest warrant from Interpol have also generated criticism.
The election results in the district of Aydınlık show that the number of valid votes (1,585) is higher than the total number of votes cast (1,460), meaning that there was a negative number of invalid/blank votes. This has raised questions about electoral conduct during the election.