Mamitu began 2010 with a career best run of 2:24:19 hours to take a marathon victory on her second outing over the distance – her win at the Dubai Marathon earned her $250,000 in prize money.[10] Her road success translated to cross country as she came second at the Ethiopian championship behind Meselech Melkamu.[11] At the 2010 IAAF World Cross Country Championships in Poland in March she improved upon her performance from the previous year, coming eighth and again taking the team silver with Ethiopia.[12] She turned to the American road circuit later that year and won the Bolder Boulder, was the runner-up at the Lilac Bloomsday Run, and had podium finishes at the Bay to Breakers and Freihofer's 5K.[4] She was invited as one of the elite women's runners at the 2010 Chicago Marathon and was sixth in a time of 2:28:29 hours.[13] As in 2010, she closed her year at the Obudu Race and was second on this occasion.[4]
She posted a time of 2:26:33 hours to win the Houston Marathon in January 2011, completing an Ethiopian sweep of the top two with Ashu Kasim.[14] She was runner-up at both the Bolder Boulder and the Bay to Breakers races, later going on to win for the first time at the Freihofer's Run for Women.[15] Her biggest achievement that year came at the Frankfurt Marathon, where she bettered the course record by nearly 90 seconds with her time of 2:21:59 hours.[16] She came ninth at the 2012 Dubai Marathon, although her finishing time of 2:24:24 was among her fastest performances.[17] She defended her title at the Freihofers' Run for Women, finishing some distance ahead of runner-up Ashu Kasim.[18] This marked the start of a dominant run on the American road circuit, where she won the Bolder Boulder, Lilac Bloomsday Run, Bay to Breakers, Peachtree Road Race and Boilermaker Road Race all in one season.[4] She returned to defend her Frankfurt Marathon title, but was beaten into third, while her compatriot Meselech Melkamu took the win.[19]
She returned to Houston in 2013 for the half marathon section of the race and won in a time of 69:53 minutes.[20] She was only 12th at the 2013 Boston Marathon, but took victories at the New York Mini 10K and BAA 10K (setting a best of 31:44 minutes). Her best marathon race that year was at the Frankfurt Marathon, where she was fourth in 2:23:23 hours.[21]
She was a podium finisher coming in third place at the TCS New York City Marathon on November 5, 2017 with a time of 2:28:08.[22]