Guelleh, 73, is facing political newcomer
Zakaria Ismail Farah, his only rival after traditional opposition parties decided to boycott the election.
A businessman specialised in the importation of cleaning products, Farah, 56, is seen by observers as unlikely to pose a significant challenge to the strongman who has been in power for 22 years.
Guelleh, flanked by his wife and government officials, wrapped up his campaign on Wednesday with a colourful final rally in a stadium packed with cheering supporters and traditional dancers.
"As I see you today in large numbers, I am sure that you will also come in large numbers to the polling stations," Guelleh said before crowds wearing tee-shirts emblazoned with his popular initials, IOG.