Lions manager Kenny Jackett, highly-regarded on Eriksson's coaching staff at Manchester City, turned him down at first after a 90-minute phone interview, but the Great Swedish Lothario's intervention prompted a change of heart.
Millwall chairman John Berylson said: "Mr Eriksson convinced him this would be a good move for Kenny and that turning around a struggling club would add to his reputation as a manager.
"So we have Sven to thank for Kenny getting us promoted. I'm sure other clubs will try and prise him away - some have tried and failed a number of times and I hope he sees his future as rising with us.
"I'm committed to Millwall - back in the States I play golf in Millwall shirts and I even sleep in a Millwall shirt. At first a lot of people said I was only interested in The Den as real estate, but we only lost once at home this season so I have no intention of tearing it down."