Answer by taking a quote from the following article:

Wilhelmus Simon Petrus Fortuijn, known as Pim Fortuyn (Dutch: ['pIm for'toeyn] ( listen); 19 February 1948 - 6 May 2002), was a Dutch politician, civil servant, sociologist, author and professor who formed his own party, Pim Fortuyn List (Lijst Pim Fortuyn or LPF) in 2002. Fortuyn was often regarded as controversial due to his outspoken views about multiculturalism, immigration and Islam in the Netherlands. He called Islam "a backward culture", and was quoted as saying that if it were legally possible, he would close the borders for Muslim immigrants. He was labelled a far-right populist by his opponents and in the media, but he fiercely rejected this label.

In 1992 Fortuyn wrote "Aan het volk van Nederland" (To the people of the Netherlands), declaring he was the successor to the charismatic but controversial 18th-century Dutch politician Joan Derk van der Capellen tot den Pol. A one-time communist and former member of the social-democratic Labour Party, Fortuyn was elected "lijsttrekker" of the newly formed Livable Netherlands party by a large majority on 26 November 2001, prior to the Dutch general election of 2002.  On 9 February 2002, he was interviewed by the Volkskrant, a Dutch newspaper (see below). His statements were considered so controversial that the party dismissed him as lijsttrekker the next day. Fortuyn had said that he favoured putting an end to Muslim immigration, if possible and wanted to abolish Article 1 of the Dutch constitution, the equality before the law. Having been rejected by Livable Netherlands, Fortuyn founded his own party Pim Fortuyn List (LPF) on 11 February 2002. Many Livable Netherlands supporters transferred their support to the new party.  Heading the list of the Livable Rotterdam party, a local issues party, he achieved a major victory in the Rotterdam municipal council elections in early March 2002. The new party won about 36% of the seats, making it the largest party in the council. For the first time since the Second World War, the Labour Party was out of power in Rotterdam.  Fortuyn's victory made him the subject of hundreds of interviews during the next three months, and he made many statements about his political ideology. In March he released his book The Mess of Eight Purple Years (De puinhopen van acht jaar Paars), which he used as his political agenda for the upcoming general election. Purple is the colour to indicate a coalition government consisting of left parties (red) and conservative-liberal parties (blue). The Netherlands had been governed by such a coalition for eight years at that time.

When did he achieve victory with his party?
he achieved a major victory in the Rotterdam municipal council elections in early March 2002.