The 29-year-old joins from Forfar Athletic and has put pen to paper on a one-year deal.
Bain began his career with Airdrie and played over 200 games for the Diamonds between 2008 and 2016.
He then switched to Forfar where he racked up a further 150-plus appearances in his four years at Station Park.
Lennon said he was delighted to recruit Bain to the Broadwood cause.
He said: “He is predominantly a right back, but is also very comfortable in a couple of other positions, which makes him a valuable asset.
“He has played over 340 games for Airdrie and Forfar combined, with the vast majority in League 1, which provides the type of experience that we need to strengthen our defensive area.
“His goals and assists record is also another factor that demonstrates he has the qualities we look for in a player in this key position, to suit our style of play.”
Lennon is still pursuing other targets as he continues to reshape his squad ahead of the new season.
Since the premature end of last season Kieran Duffie, Declan Fitzpatrick, Ross Lyon, Darren Smith and Gregg Wylde have been released while Lennon has also lost the services of Tom Lang, who has returned to parent club Dunfermline, John Rankin, who has retired, and Ray Grant and Chris McStay, who have turned down new deals
However Mark Lamont, Ally Love and Kristoffer Syvertsen have signed on again, joining Barry Cuddihy, David Goodwillie, Craig Howie, Chris Johnston, Michael McGee, Martin McNiff, David Mitchell and Scott Rumsby who were already under contract for 2020-21.