Foden stroked home in the 16th minute from Kevin De Bruyne's pass and it proved sufficient to seal a 10th successive league win for Pep Guardiola's relentless champions.
They were far from their slick best in west London, however, with Brentford always looking capable of salvaging something.
De Bruyne did hit the post after the break and both Foden and Aymeric Laporte had goals disallowed as City sought to give themselves a cushion.
But City held on with few real scares to reach 50 points from 20 games, with Chelsea on 42 from 20 and Liverpool on 41 having played one game less than the top two.
It is the fourth time Guardiola has enjoyed a 10-game winning sequence since becoming City manager.
"Round Christmas you have to keep your foot on the gas and keep focused. This team is doing that," Foden said.
Foden was left out of City's starting line-up in their two previous league games against Newcastle United and Leicester City after incurring the wrath of Guardiola for having a night on the town with team mate Jack Grealish.
Restored to the starting eleven at Brentford, the 21-year-old made amends with a finish of real quality.
Seconds after Joao Cancelo had cleared off the line to deny Brentford the lead, City went ahead in clinical fashion.
A flowing move ended with the ball played back to De Bruyne whose instinctive first-time pass picked out for the fractionally onside Foden. He feathered a volley past Alvaro Fernandez for his fifth league goal of the season.
City dominated early in the second half with Foden heading wide from another De Bruyne delivery before having a goal disallowed for offside.
Brentford rode their luck as De Bruyne smacked a left-footer against the base of the post before Laporte's majestic header was ruled out for a marginal VAR offside decision.
Despite lacking the flair that had seen them score 17 goals in their last three games, City showed they can also grind out wins when required and are beginning to look unstoppable.
Brentford remain in 14th place -- nine points above the relegation zone.