The Governor Darius Ishaku-led PDP Bayelsa State Governorship Primary Committee conducted the exercise at the Dr. Gabriel Okara Cultural Centre, Yenagoa.
The exercise, which began at 11:30pm Tuesday night ended at 5:00am Wednesday morning.
Diri, who represents Bayelsa Central at the National Assembly, defeated 19 other aspirants to emerge the PDP candidate for the forthcoming November 16 governorship election in the state.
One of the 21 aspirants, Talford Ongolo, had stepped down from the race on the eve of the primary poll.
Diri polled a total of 561 votes to win the governorship ticket of the PDP.
Former Presidential Adviser on Niger Delta Affairs, Timi Alaibe, came second with 365 votes.
Diri and Alaibe are from the same Kolokuma/Opokuma Local Government Area.
Keniebi Okoko, son of a former national President of the Ijaw National Congress and Professor of Political Science, Kimse Okoko, got third position in the primaries with 142 votes.
Diri was believed to be the preferred candidate of the state governor, Seriake Dickson, for the Restoration Caucus in the state chapter of the PDP.
Prior to the voting, delegates were accredited at the Ijaw House on the Sani Abacha Expressway from where they were conveyed to the Dr. Gabriel Okara Cultural Centre.
The exercise was monitored by officials of the Independent National Electoral Commission (INEC) led the state Resident Electoral Commissioner (REC), Monday Tom Udoh.
Ishaku said total votes cast were 1, 253 while total valid votes were 1,237 and a total of 16 invalid votes were recorded.
Ishaku, who declared Diri winner of the poll said he scored 561 votes to win the political contest.
“I, therefore, by the authority conferred on me as the chairman of this gubernatorial primary election which took place today in Yenagoa; the highest votes were scored by Senator Douye Diri.
“He has the highest votes of 561 votes. I, therefore, declare him as the winner of this gubernatorial election,” he said.