Lawmaker Korneliya Ninova on Sunday was elected head of the Bulgarian Socialist Party (BSP), the country's biggest opposition.

Apart from being the first woman to ever head the BSP, she will also go down in history as the first contender to defeat a running incumbent.

With the congress vote split 395-349 for Ninova in the runoff against Mihail Mikov, some delegates later told the media they were voting for change at a party that has steadily been losing popularity and voters.

The last few years have been difficult for the BSP, the successor to the Bulgarian Communist Party (BKP) which ruled under a one-party system during the Cold War and at the end of the 1980s had a million members (out of a population which at the time was 9 million).

It was under a socialist-dominated administration that Delyan Peevski, a controversial lawmaker from the Movement for Rights and Freedoms (DPS) and an alleged media mogul, was appointed in 2013, with the move sparking nationwide protests.

The BSP-led government stepped down in a year, at a time the party had already lost a number of elections (it had also lost the 2013 vote coming second to conservative GERB which, however, did not form a cabinet), reducing its support to less than 20% of the electorate.

On Sunday, following her victory, Prime Minister Boyko Borisov said there was no need to comment on the BSP election as the party had significatly lost its national presence by withdrawing activity from the towns and rural areas and focusing on its Sofia-based headquarters.

Ironically, it was Ninova, one of Borisov's fiercest critics in Parliament, who also advocates a return of the BSP to its traditional base.

Ninova, 47, graduated from the Sofia University with a law degree, and the first steps she made in her career were in that field; later she also became an examining magistrate.

After holding the latter office for two years -, she had a stint (March-August 1997) at then state-owned telecom BTK, and later in the same year joined a recently privatized exporting company called Technoimpex as CEO.

The move was under the administration of Ivan Kostov, who took up the Prime Minister's office in 1997 as the leader of right-wing SDS party.

In 2003, however, she joined the BSP.

It was two years later that the party won a general election, resulting in her first step into politics, when she was appointed Economy and Energy Minister Rumen Ovcharov's deputy. A scandal leading to the resignation of Ovcharov also led to her dismissal. A probe was conducted that found no evidence of wrongdoing.

Upon taking over the Deputy Energy Minister's office, she also co-headed the board of tobacco holding Bulgartabac (also state-owned at the time), a position she assumed by the summer of 2009.

She first became MP in 2009, during the GERB cabinet, but rapidly turned into one of the most vehement critics of its policies, and significantly contributed to BSP's stand as an opposition party.

Ninova also ran (but lost to Mihail Mikov) to take over the party in 2014, when a reshuffle at the top was prompted by political instability and the collapse of the then ruling coalition headed by the BSP.

She announced her bid in mid-March, counting on support from key party heavyweights such as Rumen Ovcharov himself and "popular" MPs such as Kiril Dobrev (who had been a candidate but dropped out during the Congress).

The reintroduction of a progressive tax system, which was revoked under the BSP's tenure as senior coalition partner in 2005-2009, is one of her main causes together with an improvement in a number of social rights.