The 24-year-old isn't expected to win the race but could contend for a medal.
Kenya's David Rudisha, who has been dubbed 'the best athlete you've never heard of', is expected to take gold in the race at 8pm.
Osagie's last message on Twitter this afternoon read: "Thank you to everyone for their support.. Remember to shout, curse and swear at the tv! Nothing to lose!"
Osagie has been drawn in lane number two, the furthest inside, for the final.