|IAAF World Cross Country Championships|
|1999 Belfast||Short race|
|2002 Dublin||Short race|
|1999 Johannesburg||1500 m|
|2003 Abuja||5000 m|
|2003 Hyderabad||5000 m|
His first medals came in 1998, when he took bronze and team gold at the junior race at the IAAF World Cross Country Championships and won a silver in the 5000 m at the 1998 African Championships in Athletics. With Haile Gebrselassie as his training partner, he continued to improve, winning the junior race and taking bronze in the senior short course for a medalling double at the 1999 World Cross Country Championships. He also won the 1500 metres gold medal at the All-Africa Games that year.
Mekkonen attended the 1999 and 2001 World Championships in Athletics and represented Ethiopia at the 2000 Summer Olympics, but he failed to make the podium at any of the events. His form improved in 2002 and he won the short race bronze and team silver at the World Cross Country Championships. He focused on the track in 5000 m the next year and won the 2003 All-Africa Games silver and the 2003 Afro-Asian Games gold medal. After a long time out of the spotlight of international competition he re-emerged in 2009 after switching to the half marathon and marathon.
Mekonnen came to prominence at the age of eighteen with a silver medal performance in the 5000 m at the 1998 African Championships in Athletics, finishing behind reigning world champion Daniel Komen. He followed this up with a gold and team silver in the junior race and an individual and team bronze medal in the short race at the 1999 IAAF World Cross Country Championships. He put much of his success down to the help he had received from Haile Gebrselassie, who was his training partner and mentor. He ran a world junior record in the 3000 m in Stuttgart, Germany, but this was never ratified as he did not undergo the doping controls necessary for record purposes. He finished seventh in the 5000 m at the 1999 World Championships in Athletics and closed the year with a 1500 metres gold medal at the 1999 All-Africa Games and a win at the Cross Internacional de Venta de Baños. He set an indoor world record of 8:09.66 in the two miles in Birmingham in February. However, Mekonnen only managed sixth place in the short race at the 2000 IAAF World Cross Country Championships, but again he won the team bronze with Ethiopia. He represented his country at the 2000 Summer Olympics, finishing seventh in the semi-finals of the 1500 metres.
Competing at his first IAAF World Indoor Championships, he finished seventh in the final of the 1500 m. After this he decided that he would not succeed over distance and permanently switched to the 5000 m, saying: "That’s enough for the 1500. It was tried, it didn’t work." Returning to the cross country championships, he improved to win the team silver at the 2001 edition, although he finished tenth overall. He finished eighth in the 5000 m at the 2001 World Championships in Athletics. He was selected for the 2001 IAAF Grand Prix Final, but he only managed eighth place in the 3000 m final. He also took part in the 5000 m at the 2001 Goodwill Games, just missing out on the medals in fourth. He began taking part in road races and won the Memorial Peppe Greco 10 km. He had his best ever cross country result at the 2002 edition in Belfast, winning a bronze medal for himself and helping Ethiopia to the team silver in the short race. He ran in the QSI 10 km and was second behind Haile Gebrselassie who set a world best for the distance.
At the 2003 All-Africa Games, he decided not to defend his 1500 m title and instead opted for the 5000 m and he won the silver medal, just beaten by Kenenisa Bekele. He travelled to Hyderabad in India to compete at the 2003 Afro-Asian Games, where he won the gold in the 5000 m. He took part in the 2003 International Chiba Ekiden and was the fastest runner in the second stage and helped Ethiopia to victory in the fastest ever Ekiden race.
He won the Montferland Run 15 km in 2005.
From 2008 onwards, he began to focus more on road running competitions. After a long absence from major international competition, he signed up for the 2009 IAAF World Half Marathon Championships. However, he failed to finish the race. He finished second at the Great Scottish Run behind Jason Mbote in late 2009. The following year, he took eighth place at the 2010 Paris Marathon and even though he fell over midway through the race, he recovered to set a personal best of 2:09:01. Further improvement came at the Amsterdam Marathon where, despite finishing in fifth, he ran almost a minute and a half faster than his previous best by completing the race in 2:07:37.
He cut another two seconds off his best with his winning time at the 2011 Tokyo Marathon in February. He was runner-up at the Montferland Run that year, being beaten to the title by Philip Langat. He returned to defend his title at the 2012 Tokyo Marathon, but could manage only eighth place on that occasion. on September 22, 2012 he won the heng shui marathon in 2:08.05
- 1500 metres - 3:33.14 (2000)
- One mile - 3:53.40 (2000)
- 3000 metres - 7:30.53 (2001)
- 5000 metres - 12:58.57 (2001)
- 10,000 metres - 28:01.10 (2002)
- Half marathon - 1:01:29 (2009)
- Marathon - 2:07:35 (2011)
|1998||World Cross Country Championships||Marrakech, Morocco||3rd||Junior race (8 km)||22:51|
|1st||Junior team competition||16 pts|
|World Junior Championships||Annecy, France||5th||5000 m||14:06.30|
|African Championships||Dakar, Senegal||2nd||5000 m||13:38.19|
|1999||World Cross Country Championships||Belfast, Northern Ireland||3rd||Short race (4.236 km)||12:35|
|3rd||Team competition||55 pts|
|1st||Junior race (8.012 km)||25:38|
|2nd||Junior team competition||24 pts|
|World Championships||Seville, Spain||7th||5000 m||13:18.97|
|All-Africa Games||Johannesburg, South Africa||1st||1500 m||3:39.73|
|2000||World Cross Country Championships||Vilamoura, Portugal||6th||Short race (4.18 km)||11:27|
|2nd||Team competition||46 pts|
|Summer Olympics||Sydney, Australia||7th (semis)||1500 m||3:40.92|
|2001||World Indoor Championships||Lisbon, Portugal||7th||1500 m||3:52.72|
|World Cross Country Championships||Oostende, Belgium||10th||Short race (4.1 km)||13:03|
|2nd||Team competition||51 pts|
|World Championships||Edmonton, Canada||8th||5000 m||13:20.24|
|Goodwill Games||Brisbane, Australia||4th||5000 m||15:26.70|
|2002||World Cross Country Championships||Dublin, Ireland||3rd||Short race (4.208 km)||12:20|
|2nd||Team competition||32 pts|
|2003||All-Africa Games||Abuja, Nigeria||2nd||5000 m||13:26.73|
|Afro-Asian Games||Hyderabad, India||1st||5000 m||13:49.08|
|2009||World Half Marathon Championships||Birmingham, United Kingdom||—||Half marathon||DNF|
- Minshull, Phil (1999-03-28). Hailu goes one better than Haile. IAAF. Retrieved on 2010-04-11.
- Mekonnen Hailu. IAAF. Retrieved on 2010-04-11.
- Yohannes, Sabrina (2001-03-02). Wolde heads Ethiopian team for world indoors. IAAF. Retrieved on 2010-04-11.
- Yohannes, Sabrina (2001-08-10). Mekonnen is ready to make the 5000 metres count. IAAF. Retrieved on 2010-04-11.
- Ngeny back on top. IAAF (2001-09-06). Retrieved on 2010-04-11.
- World Best and One Million Dollars for Gebrselassie. IAAF (2002-12-11). Retrieved on 2010-04-11.
- Fredericks announces retirement – African Games – Day FIVE. IAAF (2003-10-16). Retrieved on 2010-04-11.
- Nakamura, Ken & Onishi, Akihiro (2003-11-24). Ethiopians in record winning form in Chiba. IAAF. Retrieved on 2010-04-11.
- Turner, Chris (2009-10-08). MEN’s RACE PREVIEW - World Half Marathon, Birmingham 2009. IAAF. Retrieved on 2010-04-11.
- Glasgow 2009 race results. Run Glasgow. Retrieved on 2010-04-11.
- Vazel, Pierre Jean (2010-04-11). 2:22:03 World lead for Baysa, Tola improves to 2:06:37 - Paris Marathon report. IAAF. Retrieved on 2010-04-11.
- van Hemert, Wim (2010-10-17). Getu Feleke sets Amsterdam course record: 2:05:44. IAAF. Retrieved on 2010-10-20.
- Nakamura, Ken (2011-02-27). Mekonnen triumphs in Tokyo in 2:07:35. IAAF. Retrieved on 2011-02-27.
- van Hemert, Wim (2011-12-04). Langat and Afework the big winners in 's Heerenberg. IAAF. Retrieved on 2011-12-04.
- Nakamura, Ken (2012-02-26). Kipyego wins Tokyo Marathon, Gebrselassie fades to a disappointing fourth. IAAF. Retrieved on 2012-02-27.
| Men's 3000 m Best Year Performance