He began competing in international races in 2008 and finished third at the Casablanca Marathon that year, posting a time of 2:13:29. He had his first victory at the end of the year, winning the Macau Marathon in December. He opened 2009 with a second-place finish at the Marrakech Marathon in January. Yemane made significant progress at the Paris International Marathon in April that year: although he finished in fourth place, he clocked a much improved personal best of 2:06:30. He qualified to represent Ethiopia at the World Championships in Athletics and put in a strong debut performance at the 2009 World ChampionshipsMarathon race with a time of 2:08:42, just seven seconds behind bronze medallist Tsegay Kebede. Two months later he recorded his third consecutive sub-2:09 time, breaking the course record at the Gyeongju International Marathon in the process. In the 2010 season, he started by setting a new half marathon best of 1:01:50 at the Zayed International Half Marathon. He stepped back up to the full distance for the Lake Biwa Marathon and won in cold conditions, beating Tomoyuki Sato and Hendrick Ramaala to the finish. He improved further at the Prague Half Marathon with a quick run of 1:01:37 for third place, in spite of poor conditions. He was the race favourite for the Prague Marathon in May, but late entrant Eliud Kiptanui won the race instead, leaving Tsegay as runner-up with a time of 2:07:11. He was dissatisfied with the run, saying that he classified 2:05 as a good time for his ability. He ran at the Berlin Marathonin September 2010 and finished in fourth place, running 2:07:52 in wet conditions. He was among the favourites for the 2011 Tokyo Marathon but never looked likely to win the race and ended up in ninth with a comparatively slow time of 2:11:49. He was eighth at the Prague Marathon but performed well in east Asia near the end of the year, coming third at the JoongAng Seoul Marathon in a time of 2:10:47 hours in spite of poor weather, then setting a race record of 2:10:24 hours to win the Taipei Marathon. Yemane improved his personal best by a second at the 2012 Dubai Marathon, but his time of 2:06:29 hours brought him only tenth place in the quick race, which saw him beaten by eight other Ethiopians. He achieved a significantly faster time at the 2012 Rotterdam Marathon, winning the event in 2:04:48, just one second ahead of countryman Getu Feleke, and bringing himself up to eighth place on the all-time lists. The majority of his 2013 season was geared towards preparation for the 2013 World Championships Marathon, where ultimately he fell off the pace and finished in eighth with a time of 2:11:43 hours. He made a successful return to the Dutch road racing circuit by winning the Eindhoven Marathon in a time of 2:09:11 hours. In May 2014, Tsegay won the Ottawa Marathon in 2:06:54, setting a new Canadian soil record as well as the course record. He is married to Abeba Aregawi.
