Ilyin became Kazakhstan's first junior and senior weightlifting world champion when he placed first overall in the −85 kg class at the 2005 World Weightlifting Championships. He snatched 170 kg and clean and jerked 216 kg for a total of 386 kg. His total of 386 was the youth world record for the now retired −85 kg class. The next year Ilyin competed in the 94 kg class at the 2006 Junior World Weightlifting Championships, 2006 World Weightlifting Championships and 2006 Asian Games in Doha, winning all these competitions. At the 2006 Junior World Weightlifting Championships he snatched 176 kg and clean and jerked 225 kg for a total of 401 kg; Andrei Aramnau from Belarus captured the silver medal with 393 kg total with 177 kg snatch and 216 kg clean and jerk. In September 2006 Ilyin snatched 175 kg and clean and jerked 217 kg for a total of 392 kg, securing the gold medal in the −94 kg category at 2006 World Weightlifting Championships. With his final two lifts in the clean and jerk phase he attempted to set a world record with 233 kg but was unsuccessful. In December 2006 Ilyin won the −94 kg class at 2006 Asian Games, snatching 175 kg and clean and jerking 226 kg for a total of 401 kg. After a very successful year Ilyin was named 2006 IWF World Weightlifter of the Year for the second time. Ilyin competed in the −94 kg class at the 2008 Summer Olympics in Beijing and originally won the gold medal, snatching 180 kg and clean and jerking 226 kg for a total of 406 kg. In 2011, Ilyin competed in the −94 kg class at the world championships and once again won the gold medal in both the clean and jerk and the overall. He snatched 181 kg and clean and jerked 226 kg for a total of 407 kg. Ilyin originally won the gold medal at the 2012 Summer Olympics in the 94 kg category with a world and Olympic record total of 418 kg. He was successful in all three snatch attempts with lifts of 177 kg, 182 kg, and 185 kg. He was also successful in all three clean and jerk attempts with lifts of 224 kg, 228 kg, and 233 kg. His final lift of 233 kg was initially recognized as the world and Olympic record in the clean and jerk. On 14 September 2016 all of these results were annulled and his medal stripped for doping violations. In 8 November 2012 Ilyin was awarded the Olympic Council of Asia award as the best Asian athlete, along with Zulfiya Chinshanlo and Olga Rypakova. Ilyin competed in the -105 kg category at the 2014 World Weightlifting Championships held in Almaty. He snatched 183 kg, 187 kg and 190 kg, placing third. Ilyin made two out of three lifts in the clean and jerk, lifting 233 kg on his opener and on his final lift of 242 kg, breaking the clean and jerk world record and winning the competition by virtue of lighter body weight. On 12 December 2015 Ilyin competed in the Iwf Grand Prix 5th Russian Federation Presidents Cup held in Grozny. Ilyin completed two out of three lifts in the snatch, going 184 kg on his opener and 191 kg on his final attempt to secure the gold medal. In the clean and jerk Ilyin made two lifts with a third lift in hand, going 231 kg on his opener before making a 15 kg jump to break his own clean and jerk world record and successfully hitting 246 kg to win the gold medal. This total of 191/246 gave him the new total world record of 437 kg. In March 2016 Ilyin was named the IWF World Weightlifter of the Year for the fourth time in his career. In June 2016 it was announced by the IWF that retests of the samples taken from the 2012 Summer Olympics indicated that Ilyin had tested positive for prohibited substances, namely dehydrochloromethyltestosterone and stanozolol. On 14 September 2016, Ilyin was stripped of his second Olympic medal. Also in June 2016 it was announced by IWF that retests of the samples taken from 2008 Summer Olympics indicated that Ilyin had tested positive for stanozolol. If confirmed, Ilyin faced losing his first Olympic medal. Ilyin is a member of the Astana Presidential Club.
