Mari Hemmer (Norwegian: [ˈmɑ̂ːrɪ ˈhɛ̀mːər] ^ⓘ; born 20 November 1983) is a Norwegian long-track speed skater, with particular strength in the longer distances 3000 m and 5000 m. She is the Norwegian Allround Champion for 2005, 2007, 2008, 2010, the Norwegian Sprint Champion for 2005, 2009, 2010, and has also won numerous gold, silver, and bronze medals from national championships at single distances. Along with fellow skaters Maren Haugli and Hege Bøkko, Hemmer has in recent years represented Norway at the European Championships, the World Allround Championships and the World Single Distance Championships, as well as in the World Cup. Hemmer is the holder of the current Norwegian record on 10000 m.^[2]

In March 2009, Hemmer broke her own national record in the 10000 m, improving the time from 14:50.52 to 14:47.49. The feat was carried out just hours after having skated the 5000 m in 7:13.50, making her one of the few skaters ever who have run both the 5000 m and 10000 m on the same day. The time is still the current Norwegian record.^[2]

As of April 2011, Hemmer is the 3rd best ever Norwegian female skater, as per the Adelskalender, after Maren Haugli and Ida Njåtun. Her rank on the international Adelskalender, as of after the 2010–11 season, is 46.