The hosts actually took the lead through Neal Maupay's breakaway goal in the 21st minute, but it took a heroic performance from Bees keeper Mark Flekken to keep the reigning champions at bay with a string of stunning saves until Foden struck in first-half stoppage time.
Foden's goal gave City the added momentum they needed and he grabbed his second eight minutes after the break when he stole in behind Brentford's defence to glance Kevin de Bruyne's cross beyond the exposed Flekken.
Brentford, despite being dominated, had fleeting chances to level, especially when Ivan Toney volleyed over from close range, but City were vastly superior and wrapped up the win 20 minutes from time when Foden took Erling Haaland's pass in his stride to steer the ball past Flekken.
In the closing stages there was an angry bust-up between Kyle Walker and Maupay, with the former needing to be calmed down by manager Pep Guardiola, who declined to comment post match.
City kicking into gear
Manchester City may have taken until the closing moments of the first half to finally beat the outstanding Flekken, but it was no more than they deserved for peppering the Brentford goal with shots before making the breakthrough.
With Haaland still working his way back from a foot injury and not quite his usual deadly self, Foden assumed the goalscoring responsibilities with the second senior hat-trick of his career, after scoring three in the 6-3 derby win over Manchester United in October 2022.
And this was an ominous City performance, not only as they close in on top spot but also with the sight of world-class duo Haaland and De Bruyne starting a game together for the first time since the opening night of the league season at Burnley back in August.
This is traditionally the time of year when City hit top form and the statistics are starting to hint at another charge, with this their seventh successive win since claiming the Club World Cup with victory over Fluminense in late December.
City can go now top with victory over Everton at Etihad Stadium on Saturday lunchtime as their presence starts to loom even larger over the Premier League title race.
Flekken heroics not enough for Brentford
Brentford offered their usual mix of energy and defiance but were ultimately no match for Manchester City.
There is certainly no shame in that for Thomas Frank's team, and until the dying seconds of the first half, when Ethan Pinnock's misdirected header found Foden, Brentford were harbouring hopes of an unlikely victory thanks to Maupay's calm finish after collecting a long goal-kick from Flekken.
And this was thanks, above all, to a virtuoso performance from Flekken, who was magnificent as City rained in 17 shots, 10 on target, in that first 45 minutes alone.
Flekken saved twice from Julian Alvarez, blocked Haaland with his feet and also kept out Kyle Walker, Josko Gvardiol, De Bruyne and Foden before the latter finally pierced the barrier.
There was only one winner after that but there were pluses for Brentford, including a goal in a fifth successive game for striker Maupay, who continues his rebirth after a desperate struggle at Everton where he scored only one goal in 32 appearances, including 14 starts.
In the end however, City - and Foden in particular - were just too good.