Richardson joined the Power in October 2012 in the newly created role of director of coaching and strategy alongside senior coach Ken Hinkley.
Port Adelaide chief executive Keith Thomas congratulated Richardson on his appointment.
“On behalf of everyone at Port Adelaide I wish Alan all the very best in his new role as senior coach of St Kilda,” Mr Thomas said.
“Alan has been outstanding in his role as director of coaching and strategy here this season and has been important to our resurgence as a club.
“He helped develop our entire coaching group, facilitated our player leadership program and was closely involved in opposition analysis from a strategy perspective.
“Alan has been very patient in waiting for a senior coaching opportunity and now that he has his chance we hope it is a success for him and his family.
“We respect his desire to be a senior coach and wish him luck with the position.
“As a club we are all about growing our people both personally and professionally and we feel we have achieved this with Alan.
“Port Adelaide is again being seen as a club respected by others in the industry for the way we go about our work so to that end I’m also very pleased.”
STATEMENT: Alan Richardson
However, Mr Thomas expressed his disappointment with the timing of the process that led to Richardson’s departure.
“Clearly we are disappointed to lose Alan purely based on his outstanding coaching credentials,” Mr Thomas said.
“But we are also frustrated by this late development caused by St Kilda’s delayed decision-making process.
“As with any club, a significant change to our coaching structure on the eve of pre-season is disruptive to our club’s football program and planning cycle.
“But helped by the recent acquisition of Phil Walsh our football program is now very well placed to absorb this adjustment and move on and continue our momentum into 2014.”
