Jacob Thorbjørn Olesen (born 21 December 1989) is a Danish professional golfer who plays on the European Tour, where he has won five times including the 2016 Turkish Airlines Open and the 2018 Italian Open. He has also won two important pairs events, representing Denmark, the 2016 World Cup of Golf with Søren Kjeldsen and the 2017 GolfSixes with Lucas Bjerregaard.
Olesen turned professional in 2008. He finished in fourth place on the third tier Nordic League rankings in 2009, having won three tournaments, to graduate to Europe's second tier Challenge Tour for 2010. During his début season he claimed his first Challenge Tour title at The Princess, held in Sweden at the beginning of July. He finished third in the 2010 Challenge Tour ranking, earning him full exemption (category 10b) for the 2011 European Tour.
In December 2010, Olesen tied for second place at the Alfred Dunhill Championship, the first tournament of the 2011 European Tour season. This was equaled in June 2011, when Olesen tied for second at the BMW Italian Open in Turin, mostly due to a 10-under-par round of 62 on the final day, but still coming up short by one stroke of Englishman Robert Rock. The following month Olesen finished in a tie for second again at the Alstom Open de France when he bogeyed the last hole to finish one stroke behind Thomas Levet. With this finish, Olesen qualified for The 2011 Open Championship, his first major.