Portillo has behaved like a political chameleon, moving from the left to the far right with little damage to his reputation. Sympathy for the left, he explained, was rooted in youthful romanticism. Later, he came to describe himself as a social democrat sensitive to the needs of the poor. But it was his alliance with the far right that brought him to power. In 1995, former dictator Efraín Ríos Montt (1982–83) invited Portillo to join his Guatemalan Republican Front (FRG). At the time, Portillo was a Christian Democrat. Montt had been barred from running for the presidency because of his role as former dictator, and he needed a presidential candidate to represent his party. Portillo did well in the first round of the presidential election, receiving 20% of the vote. In the January 1996 runoff election, Alvaro Arzú beat Portillo by just 30,000 votes. Portillo remained a member of the FRG, and campaigned vigorously for the 1999 contest.
During the 1990s, Montt, secretary-general of the FRG, had come increasingly under criticism for violation of human rights during his dictatorship. The country's Historical Clarification Commission in 1999 said the military had committed acts of genocide during Montt's rule. Yet, among many Guatemalans, Montt had wide appeal and was seen as someone who was committed to order. Portillo could not escape Montt's shadow even though he was portrayed as leading the more liberal faction of the FRG party. Portillo insisted he was not Montt's puppet and would not fall under his influence if elected president. With a populist law and order campaign, and relentless attacks against PAN, Portillo became the candidate to beat in the November 1999 election. But Portillo, and PAN candidate Oscar Berger, a businessman and former Guatemala City mayor, failed to get 50% of the vote, forcing a runoff election a month later. Rather than being hurt by his ties to Montt and the Mexico murders, support for Portillo only grew. In the December runoff election, Portillo received nearly 69% of the vote. He was inaugurated in January 2000.