[28] With the highest approval rating in the history of the country at one time, President Luiz Inácio Lula da Silva was PT's most prominent member.

The party has been involved in a number of corruption scandals since Lula first came to power and saw its popular support plummet between 2015 and 2020, with presidential approval ratings falling from over 80% to 9%[30] and successive reductions in all elected offices since 2014.

[35] The party emerged as a result of the approach between the labor movements in the ABC Region such as the Conferência das Classes Trabalhadoras (Conclat), later developed into the Central Única dos Trabalhadores (CUT) which carried major strikes from 1978 to 1980; and the old Brazilian left-wing, whose proponents, many of whom were journalists, intellectuals, artists and union organizers, were returning from exile with the 1979 Amnesty law, many of them having endured imprisonment and torture at the hands of the military regime[36] in addition to years of exile.

[39] The first membership card belonged to art critic and former Trotskyist activist Mário Pedrosa, followed by literary scholar Antonio Candido and historian Sérgio Buarque de Holanda.

Since 1988, the Workers' Party has grown in popularity on the national stage by winning the elections in many of the largest Brazilian cities, such as São Paulo, Fortaleza, Belo Horizonte, Porto Alegre and Goiânia as well as in some important states, such as Rio Grande do Sul, Espírito Santo and the Federal District.

During the time it governed Porto Alegre, it implemented measures such as a progressive tax reform, involving the rich being taxed more highly to fund basic services for the poor, and the development of new institutions of genuine popular participation which gave, according to one study, "real decision-making power to civil society and involving a large number of civil organizations – from neighbourhood groups to non-governmental organisations (NGOs), and from cultural groups to education, health and housing pressure groups – in running the city.

As Minister of Economy, Cardoso created the Real Plan, which established the new currency and subsequently ended inflation and provided economic stability.

Candidates supported by the party won the race in Amapá, Ceará, Espírito Santo, Maranhão, Mato Grosso, Pernambuco, Piauí and Rio de Janeiro, which means that PT would participate in 13 out of 27 state governorships.

[50] For example, at the Brazilian Constituent Assembly of 1988 it advocated repudiation of Brazil's external debt, nationalization of the country's banks and mineral wealth and a radical land reform.

[50] In addition, as a form of protest and as a signal that the party did not fully accept the "rules of the game" PT's delegates refused to sign the draft constitution.

[50] In 1994, Lula ran for the presidency again and during his campaign dismissed Fernando Henrique Cardoso's recently implemented Real Plan as an "electoral swindle".

[50] The resolutions from the 1994 National Meeting condemned the "control by the dominant classes over the means of production" and reaffirmed the party's "commitment to socialism".

[50] PT's Program of Government that year also committed the party to "anti-monopolist, anti-latifúndio, and anti-imperialist change [...] as part of a long-term strategy to construct an alternative to capitalism", statements that "sent shivers down the spine of the international financial community".

[50] The resolution adopted at its 10th National Meeting in 1995 stated that "our 1994 defeat invites a cruel reflection about our image in society, about the external impact of our internal battles, [and] about our ideological and political ambiguities".

[51] He also accepted some of the liberal reforms from the Cardoso government, meaning that the party program was now de facto centre-left and social democratic in its ideology.

The socialism of PT appealed to the Brazilian Catholic left, who was heavily influenced by liberation theology and believed that Marxism and Political Catholicism complemented one another.

Liberationist bishop Mauro Morelli served as president of the National Council for Food Security, and later became a political advisor of Lula.

The PT mayor and Catholic lawyer Patrus Ananias became famous through his administration in Belo Horizonte, which became distinguished for its church-coordinated work against hunger and poverty.

Liberation theologist Frei Betto also served as Lula's special adviser, and the faction also played a crucial role in the education policy of the party and the 2010 anti-corruption "clean slate" law.

[53] The PT's close relationship with Brazil's progressive Catholic Church continues to influence the rherotic of the party, with its politicians referring concepts from liberation theology.

Fernando Haddad, the candidate seeking reelection, stayed in a distant second place, with 36 percentual points below the winner João Doria.

PT had a strong electoral stronghold in North Brazil and in the Amazonian region; The party triumphed in every state governorship in Acre from 1990 to 2018.

Roraima, which the impact of the controversy about the indigenous territory of Raposa Serra do Sol, which former President Lula gave strong support despite the opposition of the non-indigenous people; and Rondônia, which had a large population of evangelicals and south/southeastern migrants, also show reservations about the party.

PT and its allies was able to make big gains in north and northeast regions of Brazil even in times which the party was in crisis, like in the last mayoral elections.

Despite this, the state's capital Salvador is governed by ACM Neto, a leading member of DEM and grandson of Antonio Carlos Magalhães.

These struggles have fueled public debates, the worst of which had its climax in December 2003, when four dissident legislators were expelled from the party for voting against Social Insurance Reform.

[56] Among these members were congressman João Batista Oliveira de Araujo (known as Babá) and senator Heloísa Helena, who formed the Socialism and Liberty Party (Partido Socialismo e Liberdade − PSOL) in June 2004 and ran for president in 2006, becoming at the time the woman who had garnered the most votes in Brazilian history.

In another move, 112 members of the radical wing of the party announced they were abandoning PT in the World Social Forum in Porto Alegre on 30 January 2005.

As a result, Berzoini left the coordination of Lula's re-election after allegedly using PT's budget (which is partially state-funded through party allowances) to purchase, from a confessed fraudster, a dossier that would be used to attack political adversaries.

The investigation of a series of crimes, such corruption and money laundering, led to the arrest of the party's treasurer João Vaccari Neto and his sister-in-law.