Mr Oti is a former foreign affairs minister and more recently served as the country's ambassador to Fiji.
There were 48 secret ballots cast, 30 were in favour of Mr Oti, 15 went to the only other nominee and former speaker Ajilon Jasper Nasiu.
Three ballots were spoilt and two MPs were absent.
Only one nominee was put forward for the deputy speaker's post, Stanley Festus Sofu, the MP for East Kwaio.
At the end of today's session the prime minister Manasseh Sogavare is to seek a special adjournment of parliament until 4 June.