Óskar opened his first restaurant, Argentína steikhús, in 1990, which quickly became the first and most popular steakhouse in Reykjavík. He successfully managed the restaurant for 15 years before relocating to London, where he played a role in Texture restaurant, the first Icelandic-run Michelin-starred establishment, and 28/50 wine bar.

Óskar then ventured to Barcelona, engaging in various aspects of the hospitality industry. After his international endeavours, he returned to Iceland, where he, along with his wife and two children has been operating Finnsson Bistro for the past three years.