Colonel Ränisoo volunteered into conscription service in February 1991 and started his service in Estonian Border Guard. Through the service in Border Guard Colonel Ränisoo rose to the position of staff officer in Analysis and Planning Department of Border Guard. In 2004 he was assigned to the Estonian Defence Forces (EDF). In 2005/06 Colonel Ränisoo served in Iraq and in March 2007 he was appointed as Commander of MI Battalion of the EDF. In July 2010 Colonel Ränisoo graduated from the Joint Services Command and Staff College in the United Kingdom and was at first appointed as Chief of Analysis and Planning Department and in June 2011 started serving as Chief of Logistic Department of the EDF HQ. In 2014 he was reassigned to the MOD and appointed as Estonian Defence Attaché to the United Kingdom until July 2017.

Colonel Ränisoo has earned his Bachelor's degree and Master’s degree from Finnish National Defence University.

Colonel Ränisoo is married to Riia and is a father of five children. He enjoys reading, architecture and running.