John McGinn opened the scoring for the Buddies before the break and Paul McGowan added a second as they moved 12 points above rock-bottom Hearts.
Lennon was delighted with St Mirren's first Scottish Premiership win and praised his players for pulling together during a tough spell.
He said: "The character has been in question, it has been thrown at us in recent weeks, myself and the character of my players, and I am glad at times like this that it's character that is required because I certainly know I have it in abundance in that dressing room.
"Where we have been, they say that lean spells in football are character-building exercises and I believe it reveals the character of the individual.
"I certainly know I'm a fighter and those guys in there are fighters.
"We were looking to take that wee bit of confidence from Monday night's game and I thought we carried that on and we finished that by picking up all three points.
"I'm delighted for them and the supporters.
"We were certainly going to be up against it from the outset in terms of the atmosphere, the media, the 15,000 fans that were in here, from the Hearts players.
"Everyone expected us to come here and crumble and we stood up and were counted.
Lennon has faced speculation about his future, but insists there have been only brief discussions with directors about his job.
"There have been a lot of questions thrown about my time as manager," he said.
"I discussed one meeting with my chairman over this, and that was three weeks ago.
"Other than that, it has been business as usual.
"I have a board of directors that are very passionate supporters. They feel the same anger and hurt as we do.
"But in the three years I have been here, the board know the character of Danny Lennon. They also know the character, hunger and the belief that they have in the group of players we have here."
Hearts manager Gary Locke felt his side paid the price for letting their standards slip in the first-half.
"I thought we started reasonably well, we were on the front foot, passing it well and then the last 25 minutes of the half we didn't play well enough," he said.
"It's as simple as that, I am not going to sit here and make excuses.
"But it's probably the first time this season that I could say that. The boys have been brilliant up till now."
Locke admitted he must raise his team's morale ahead of their trip to Motherwell in a fortnight.
"I said before the game there is still a long way to go after today," he said.
"Obviously we would have liked to have won the game and put the pressure on St Mirren.
"There were defining moments in the game, Callum has a wee chance at 1-0 and they go right up the park and score.
"The boys are very down, but, with having such a young team, we said at the start of the season it was going to be a big ask and after today it's not going to be any different."