Lennon, who has led Cowdenbeath to back-to-back promotions, was only interviewed for the job on Friday and was offered the job within 24 hours. Their quickly arose a problem over compensation - namely that the Blue Brazil actually wanted some - but that was finally resolved this morning. A friendly between the two sides at Central Park will almost certainly be part of the deal.
Lennon, who is 40, has only been a manager for two seasons and has had a successful time with the Fife outfit. His appointment is a major gamble by the Saints board, but the same could have been said for appointing Willie McStay or Tommy Wilson, who were also linked with the job. Craig Levein and Mixu Paatelainen have also done well after starting their managerial careers with Cowdenbeath, so hopefully Lennon will follow in their footsteps.
He was a late candidate for the job, and when Mirren Mad weighed up the various possibilities the day Gus MacPherson was sacked we only classed him as a "rank outsider". It will be interesting to know if he was the first choice, and the quick turn of events in the last few days suggests he may not have been.
The midfielder had a lengthy career, playing for Hibs, Raith Rovers and Partick Thistle among many other clubs, and famously scored the goal that gave Raith a half time lead away to Bayern Munich. He worked with a tiny budget at Cowdenbeath so, while he won't have much money with us, what we have will seem like millions compared to what he had before!
There's no news yet on how long Lennon's contract is, or who his assistant will be. Early indications suggest it will be Saints coach Stuart Balmer, although there is a chance Iain Jenkins could move across from Cowdenbeath. It's unlikely Andy Millen will be staying at the club for much longer.
More will be revealed at tomorrow's press conference and we'll have an update on things tomorrow evening, before analysing the various implications of this decision later in the week.
Welcome to St. Mirren Danny and good luck - because you're going to need it!