An assistant to dual Hawthorn premiership coach Alastair Clarkson since 2010, Simpson has been viewed as a senior coach in waiting and impressed the Eagles in his interviews this week.
A two time premiership player with North Melbourne, he played 306 games with the Kangaroos and stepped straight into coaching when he retired at the end of the 2009 season.
The 37-year-old will take over from John Worsfold, who stood down at the end of the 2013 season after the club fell from premiership favouritism to a finish of 13th, managing just nine wins.
The original pool of 14 candidates had been whittled down this week, with the Eagles forced to wait for the Dockers and Hawks to finish their campaigns before formal interviews started.
It is understood highly rated assistant Scott Burns was told earlier in the week he was no longer in the running, with a decision left between the final two.
Sumich pushed close to the senior position after a two-year period under Ross Lyon at Fremantle, where his stocks appear to have been boosted significantly.
With the Gillette Trade and Free Agency Period set to launch on Friday, the Eagles needed to appoint their senior coach to contribute to list management decisions.
It is believed midfielder Daniel Kerr, who is contracted for 2014, won't make a call on his playing future until he has spoken to the new coach.