* Presidential vote to be decided in May 18 second round
* PAIGC party secures majority in parliament vote
* Pressure on country to complete return to civilian rule (Writes through with details, reaction)
By Bate Felix and Alberto Dabo
BISSAU, April 16 (Reuters) - Jose Mario Vaz, Guinea-Bissau's former finance minister, will face Nuno Gomes Nabiam, a candidate seen closest to the army, in a May 18 presidential run-off due to complete the country's return to civilian rule.
The presidential and parliamentary vote is meant to offer the nation a fresh start after decades of instability since independence from Portugal. Its last vote in 2012 was abandoned after the military seized power between rounds of voting.
"Guinea-Bissau citizens have given a strong signal to the political class in coming out in huge numbers to exercise their civic rights," Augusto Mendes head of the election commission said on Wednesday, referring to a turnout of over 80 percent.
Vaz, candidate of the dominant party African Party for the Independence of Guinea and Cape Verde (PAIGC), secured 40.99 percent of the votes in the first round, according to election commission figures.
Nabiam, the former chair of Bissau's civil aviation agency, came second with 25.14 percent, the figures showed. Nabiam comes from the Balanta ethnic group and is seen as having the support of the army, which has a long history of meddling in politics.
Paulo Gomes, a former World Bank executive and newcomer to Bissau politics, came third with just under 10 percent.
Results from the parliamentary vote showed that the PAIGC won a majority, securing 55 of the 100 available seats. The PRS, PAIGC's traditional rival, came second with 41 seats.
"These results, if managed well by particularly the leaders of the two main political parties, will ensure that Guinea-Bissau finally has the stability that is essential for structural reforms in all sectors," Jose Ramos-Horta, U.N. Special Representative in Guinea-Bissau, said.
Weak state institutions, along with its array of islands and unpoliced mangrove creeks, have made the country a paradise for smugglers of Latin American cocaine destined for Europe.
Senior figures in the military have been linked to the trade and army chief General Antonio Indjai was accused by a federal grand jury in New York on cocaine and weapons-trafficking charges.
He denies the charges but was targeted in a U.S. sting operation in 2013, a year after he led the country's last coup.
No elected leader has completed a five-year term in Guinea-Bissau and analysts say donors and regional powers who have been bankrolling the interim administration are frustrated with the recurrent crises.
"I have had talks with the two main contenders and I'm confident that they will continue the same climate of civility," Ramos-Horta said.
Whoever wins the race will have to undertake sweeping reforms in almost every ministry, particularly finance and interior, if they are to tackle rampant graft and a sclerotic administration, according to a U.N. strategy document obtained by Reuters. (Writing by David Lewis; Editing by Eric Walsh)