Hart, who played in three premierships with the Brisbane Lions – which included the 2001 Norm Smith medal – reunites with Power coach Ken Hinkley who he worked with at the Suns.
When Richardson departed to assume the top job at St Kilda, the Power said they were "underwhelmed" by the quality of candidates to fill the role.
Hart and Hinkley are obviously men cut from the same cloth.
They share a strong belief in 'people first' philosophy; Hart saying it was crucial for success.
Having declared himself a people person and the 'right man' to lead the Power on his first day as coach, Hinkley said the club had recruited a strong character in Hart.
"Shaun's an incredibly highly regarded person with everyone that's been in contact with him and I don't just say football, I say everyone that's been involved with Shaun Hart will tell you he's just an amazing person," Hinkley said on Friday.
"He's passionate, he's a hard worker and he knows exactly what it is he stands for and I think that's really important.
"We talk about bringing quality and character to our football club, that's the number one thing we want to bring, and we've achieved that in spades with Shaun."
Hart spent five years with the Suns, and has been the club's reserves coach since 2011.
Although it was a challenge to leave Queensland, his home of 25 years, Hart said the opportunity to join Hinkley and the Power was too good to refuse.
"Ken Hinkley is a brilliant operator and to work with him and to have that opportunity presented to me … it was just too good to step into," Hart said.
"I thought this was a footy club going somewhere.
"He and I share very similar beliefs about how important people are and that's what I intend to bring over to Port Adelaide – a love for people."
Gold Coast CEO Travis Auld praised Hart's contribution to the Suns.
"Releasing Shaun from his contract was a difficult decision and one made after considerable thought and consultation," Auld said in a statement.
"In the end we agreed we wouldn't be allowing Shaun to develop as a person and a coach if we restricted him from accepting this role with significantly greater responsibilities.
"Also, with our structure and current personnel, it is also highly unlikely that we would be in a position to offer Shaun similar experience in the near future."
Hart will start his new role with the Power immediately.
Twitter: @AFL_BenGuthrie
