The Scottish-born batsman began to make his mark at Durham in 2003 when he made five one-day appearances.
Coetzer was handed his first-class debut the following year when he was part of Scotland's victorious Intercontinental Cup squad, scoring 133 not out in the semi-final against Kenya. He also captained Scotland in the Under-19 World Cup in 2004.
He signed a professional contract with Durham in October 2005.
Coetzer had one of the best seasons of his career in 2007 when he helped Durham to second place in the LV County Championship, ending fourth in their batting averages, including a score of 142.
He hit an important fifth in Durham’s Friends Provident Trophy final win against Hampshire and was also Durham's second leading run-scorer in the NatWest Pro40 with 310. In addition to this he was called up to play against Pakistan in June 2007.
2008 proved to be a less productive season with Durham although he continued his Scotland career, making his one-day international and Twenty20 international debuts.
He continued to represent his country and played a part in the ICC World T20 in June 2009 in England.
However his form for Durham was his main concern, and with Mark Stoneman failing to secure a place at the top of the order in four-day cricket Coetzer duly took his chance with a solid 107 in the game that clinched the LV= County Championship title against Nottinghamshire at the Riverside.
His 107 was also part of a colossal, club-record opening stand of 314 with Michael Di Venuto, a feat that was one run behind the county's record all-time stand between Dale Benkenstein and Ottis Gibson.