The diminutive attacking midfielder has gone from Hoops reject to Saints hero – and forced himself into the frame for a Scotland call-up in the process.
McGowan (left) is the current SPL player of the month, and Lennon needs no reminding what a threat he can be to Celtic's title charge.
The Parkhead boss believes the difficult decision made to end McGowan's six-year career at Parkhead was correct – for all parties involved.
And he is delighted to see the 24-year-old grab a second chance to make his mark in the SPL. Lennon said: "I had Paul for a year at development level, and he was excellent.
"He played a few games that season under Tony Mowbray. But you can't play every kid, and you can't play them every week.
"What we had to do was make a decision on what was best for Paul's future, in terms of do we keep him another year and he plays a bit part, or does he go and further his career elsewhere?
"It was a tough decision to make. But I think, for the benefit of the player, we made the right one."
Lennon has continued to watch McGowan – who was previously on loan at Hamilton, Morton and St Mirren – put down new roots and flourish.
"It does not surprise me he is doing so well because he is a great kid with a superb attitude to the game, and he works very, very hard," said the Celtic manager.
"I'm delighted for him and delighted to see he has played consistently well.
"We just felt that, with the players we wanted to bring in, his progress would have been stunted here.
"So, to be fair to the club, we've made the right decision on Paul's behalf."
No-one at Celtic needs any reminding it was at New St Mirren Park that the unhappy 10-month reign of Lennon's predecessor, Mowbray, finally came crashing to an end with an embarassing 4-0 defeat.
In the 22 months since, the new boss has re-energised the club, and the team he has built can go five points clear of nearest title challangers Rangers if they win the lunchtime kick-off.
But Lennon knows McGowan and Co. will fancy their chances to bring this winning run – their longest in the league since 2008-09 – to a halt. He said: "Danny Lennon has bought well.
"They have beaten Rangers there recently, so they are capable of beating anyone at home.
"But, our form against St Mirren over the past couple of years has been good, so we would like to maintain that."