In her first major test outside of Ethiopia, Kalkidan won the silver medal over 1500m at the 2008 IAAF World Junior Championships in Bydgoszcz, Poland. A year later, Kalkidan dropped more than seven seconds off her 1500m lifetime best, a performance that earned her a spot representing Ethiopia at the 2009 IAAF World Championships in Berlin, where the eighteen year old qualified for the final (the youngest in the field by five years).
Fewer than six months after her first appearance at the World Championships, Kalkidan began rewriting the age group record books. At the GE Galan in Stockholm, she broke the World Junior Indoor Record for 1500m, and ten days later, ran 4:24.10 in Birmingham to obliterate the thirty year old World Junior best for the mile. Kalkidan capped off her winter at the IAAF World Indoor Championships, where she upset the defending champion to win her first international gold medal.
After ending her 2011 season with a respectable fifth place finish in the 1500m final at the IAAF World Champioinships in Daegu, South Korea, Kalkidan suffered a serious Achilles tendon injury early in 2012 campaign, forcing her to curtail her Olympic preparations and undergo surgery. The recovery lasted well into 2013, and Kalkidan was able to resume full training and racing in 2014.
In September 2013, Kalkidan became a citizen of the Kingdom of Bahrain.