Frawley, 51, was appointed as a specialist backline and key position coach by Hawthorn but had a change of heart over the weekend.
His former club had been in contact for a while about the prospect of him re-entering the coaching world, but couldn't offer anything solid until Luke Beveridge confirmed he would head to the Western Bulldogs last week.
Beveridge was appointed as the Dogs’ senior coach on Friday and went with the Saints' blessing, despite having not officially started at Seaford after accepting the director of coaching role mid-year.
Frawley was told of the Saints' position as he stood in the Hawthorn car park on Friday, but needed little time to decide.
"It didn't take too long, once I had a chat to Matt [Finnis], Andrew Thompson and Richo over the weekend … I'm really rapt to be here," Frawley said on Monday, as the Saints' senior players started pre-season training.
"I'd like to thank the Hawthorn football club for what was going to be a good opportunity as well.
"That's what happens in football sometimes, it's a moving beast, it never stands still.
"It's been a bit of a whirlwind weekend, to be honest."
Some of the players Frawley will be working with ran laps as the former club captain and Richmond senior coach was unveiled.
Frawley said the prospect of working with those players, plus the likes of Josh Bruce and youngsters set to be recruited in next Thursday's NAB AFL Draft, swayed him to come to Seaford.
"It was the thing that got me excited, to be part of something that's growing and building, and in two or three years' time you'll see the Saints where they should be and it's back in finals, and hopefully I can play a small part in that," he said.
"There's going to be bumps along the road. It's a very young group and with a young group you do get a few troughs and a few highs so I'm really looking forward to being a steadying influence around the playing group and the coaches as well."
Frawley was Richmond's senior coach from 2000 until his sacking in 2004 and also has experience as an assistant at Collingwood and Hawthorn.
He has also been CEO of the AFL Coaches Association and was inducted into the St Kilda Hall of Fame in 2007.
Now, he will work at the club he played 240 games for between 1984 and 1995, and was excited to be back at St Kilda in an official role after a 19-year absence.
"Defence wins premierships and attack entertains – that's probably one thing I'll bring to the club," he said.
"Sometimes you've just got to find a way and I think it's exciting to be here at a time where St Kilda are really building for the future.
"To get back coaching is something I've always wanted to do, and to be able to work in the media and help the Saints, I think it's a great balance for me."
Saints CEO Matt Finnis said it was a "thrill" for the club to appoint someone held in such high regard who had been targeted by coach Alan Richardson.
"Richo as our senior coach is determined to bring in quality people to our club and develop our young players with the right skills to be competitive," Finnis said.
"We also want them to develop the right values and what it takes to play AFL footy at the highest level and I can't think of a better person to bring into our club to support that."
The Saints will start interviewing shortlisted candidates for their vacant general manager of football performance role this week.
It is likely that the duties Beveridge was set to fill will be absorbed by that role.