Unnur Birna Vilhjálmsdóttir won Miss Iceland 2005 and later won Miss World 2005 pageant.
She was crowned Miss World 2005 on 10 December 2005, in the Beauty Crown Theatre located in the Chinese beach city of Sanya, by the reigning beauty queen, 2004's Miss Peru Maju Mantilla.
Mexico (Dafne Molina Lona) and Puerto Rico (Ingrid Marie Rivera) were the first and second runners up. Other contestants who made it into the final six were Miss Italy (Sofia Bruscoli), Miss Korea (Oh Eun-young) and Miss Tanzania (Nancy Abraham Sumari).
Her mother, Unnur Steinsson, won the Miss Iceland pageant in 1983 and was a finalist at the Miss World 1983 pageant. Unnur's mother was 3–4 months pregnant during the pageant. This was against the pageant rules and warrants disqualification. However, this was not found out until after the pageant was over. Unnur is the third Miss World from Iceland, the former two were Linda Pétursdóttir in 1988 and Hólmfríður Karlsdóttir in 1985.
Unnur Birna's reign as Miss World was the shortest ever, which only lasted nine months since the 2006 edition was scheduled in September. During her reign, she traveled to the United Kingdom, the United States, Iceland, Poland, Sweden, China, Brazil and many more countries.
She crowned her successor, Ta?ána Kucha?ová of Czech Republic, the next Miss World on 30 September 2006.