She was wearing a light beige dress. The closed-door meeting was expected to touch on the insurgency in Thailand's Muslim South, where near-daily attacks have left thousands dead, Agence France-Presse reported from Bandar Seri Begawan.
Before leaving Bangkok, Yingluck said she expected to discuss with the sultan ways to strengthen cooperation between the two countries, including the exchange of knowledge on agriculture and halal food.
She said Brunei was a member of the Organisation of the Islamic Conference (OIC) and Thailand could discuss opportunities for cooperation in exports and investments in halal food to Muslim countries. The discussion would also touch on sending Thai labourers to work in Brunei.
She denied that her brother, Thaksin, would also be in Brunei during her visit.
Government spokeswoman Thitima Chaisang said earlier "Thailand will thank Brunei ... for supporting Thailand and helping to explain the problem of unrest in the South to other Muslim countries so Thailand isn't blamed," she said. The PM was accompanied by Foreign Minister Surapong Towichukchaikul. Yingluck is scheduled to make her introductory visit to Indonesia tomorrow, followed by Cambodia on Thursday and Laos the following day.
The PM will seek the release of two Thai activists, Veera Somkwamkid and Ratree Pipattanapaiboon, now detained in Cambodia.
Meanwhile, Thaksin's spokesman Noppadon Pattama said yesterday that the fugitive former premier would travel to Phnom Penh on September 19 to give a lecture. However, Thaksin will leave before September 24, when the red shirts play a friendly football match with Cambodian leaders.