The midfielder scored his first goal for Albion in the 1-0 victory at the Hawthorns on Saturday, just their second win in 10 Premier League games.
It eased the pressure on head coach Alan Irvine after fans had started calling for the axe and lifted the Baggies to 14th in the table.
“We knew if we won the local derby it would catapult us up the league, get everyone back on side, get the fans back on side, because we need the fans, we need everyone at the club,” said Gardner, who started his career at Villa.
“We got the whole team, the whole club back together.
“This win can have a really galvanising effect, definitely. The fans, seeing the work rate we are putting in, seeing we are not hiding
“It is a platform to build on. It’s four points from two games and we can really push on now.”
Gardner celebrated his goal with Irvine and also handed his shirt to young fan Rui Roper at the end of the game.
Defeat ended Villa’s five-game unbeaten run and they will have to deal with suspensions for Kieran Richardson — after he was sent off — and Alan Hutton and Tom Cleverley after they received their fifth bookings of the season.
Fabian Delph and Ron Vlaar returned from injury but boss Paul Lambert knows they need more depth.
He said: “I don’t think we have the strongest (squad depth), but we’ve got Fabian back and (Philippe) Senderos is close.
Vlaar returned as a late substitute but Lambert insisted his skipper is not guaranteed a place after the form of Jores Okore and Ireland international Ciaran Clark.
He said: “The really pleasing thing is that Okore had 14 months out and is coming in like this, and Ciaran looks outstanding.
“I think he has always been up and down but playing the way he is the best I’ve seen him.
WEST BROM: Foster, Wisdom, McAuley, Lescott, Pocognoli, Sessegnon, Morrison, Dorrans (Berahino 70), Varela, Gardner, Ideye.
ASTON VILLA: Guzan, Hutton, Okore, Clark, Cissokho (Weimann 78), Cleverley, Sanchez (Vlaar 78), Richardson, N’Zogbia (Delph 46), Benteke, Agbonlahor.
Referee: Mike Dean.