Hughes, who is waiting to stand trial on charges of causing death by dangerous driving and leaving the scene of an accident, stabbed home Albion's 85th minute winner to cap a dramatic finale.
Before Hughes struck, Albion had looked set to have to settle for a point after Cardiff substitute Alan Lee cancelled out Neil Clement's opener just four minutes after being sent on.
But Hughes' late strike, his second goal in successive home games, kept Albion firmly on course for automatic promotion.
Albion also owed their success to an impressive display from goalkeeper Joe Murphy who was making his home debut fully 18 months after he joined the club from Tranmere Rovers.
The Republic of Ireland international was called-up to replace the injured Russell Hoult and kept a dangerous Cardiff side at bay.
Cardiff were also indebted to their own goalkeeper, Martyn Margetson, for a series of impressive saves.
But Cardiff, beaten for only the sixth time in 16 away games this season, paid the price for failing to make their early pressure pay.
Albion manager Gary Megson had demanded a positive response after the 3-0 defeat at Preston in their previous match and he said: "There was a lot of effort and drive from the players.
"Lee Hughes seems to have that sixth sense that some strikers have when he pops up at just the right time.
"We are now entering what I feel is the most important three months in the history of the club.
"We can really push on now and put the club where they have only been once in the last 25 years and start moving in a different direction."
Cardiff boss Lennie Lawrence admitted that his side should have made more of their early pressure and he said: "When you come to a club like West Brom you will get three or four chances and you have to take them.
"We had two good early chances and we did not take them.
"We played to our maximum but West Brom have the ability to grind out a result and at the moment we do not.
"I felt that we deserved to draw the game as we matched West Brom in all areas of the field. But we just paid the price for not taking those chances."
Murphy was thrust quickly into action - after just 58 seconds - and settled his nerves with an impressive reflex save from City's leading scorer, Robert Earnshaw.
Paul Parry showed the Albion right-back Bernt Haas a clean pair of heels and whipped in a cross to the feet of Earnshaw.
The Welsh international was just six yards from goal but Murphy was able to smother his shot on the line.
Cardiff really gave Murphy a tough Hawthorns baptism in the opening exchanges and the 22-year-old had to be alert to hold a long-range drive from Earnshaw and also punch the ball clear from Cardiff forward Peter Thorne.
It took Albion fully 20 minutes to get into the game and when they did they were also frustrated by some goalkeeping heroics.
While Murphy had denied Cardiff, his opposite number, Margetson, proved to be a thorn in Albion's side.
Albion peppered his goal from long-range, but the former Welsh under-21 international proved to be more than equal to the task.
In particular, Margetson denied the Albion midfielder Clement.
The former Chelsea trainee saw his 20th minute header saved by Margetson and then had a 35-yard drive beaten away by the former Manchester City keeper.
Margetson also turned a shot from Albion midfielder Mark Kinsella around the post before collecting another cross-shot from Clement.
When Albion finally did find a way past the 32-year-old, they were inches away from taking the lead.
A crude challenge from Richard Langley sent Albion midfielder Jason Koumas crashing to the ground 20 yards from goal on the stroke of half-time.
Koumas picked himself up to take the free-kick himself. His right-foot curler left Margetson rooted to his line, but the ball flew just past the far post.
Having withstood so much pressure, it seemed only a matter of time before Albion's persistence paid off and that proved to be the case ten minutes into the second half.
Cardiff were left fuming when Rhys Weston was adjudged to have fouled striker Geoff Horsfield on the right-hand edge of the area.
Koumas lifted another free-kick into the area that flew straight to the head of Clement who was finally rewarded for his earlier good play when he rose above the Cardiff defence to power the ball past Margetson from 12 yards.
Having worked so hard to break the deadlock Albion then threatened to undo all their earlier good play with three minutes of madness.
Murphy had to ride his luck after 59 minutes when he raced out of his goal to try and clear the ball and was left in no-man's land when his clearance was collected by Parry.
Parry had an unprotected goal to aim at but drove his angled shot just wide.
Murphy then made amends for his earlier error in the 62nd minute when he did well to beat away a close-range header from Richard Langley.
But there was nothing that he could do when Albion were caught napping 11 minutes from time.
Just as Cardiff had been undone by a free-kick, Albion suffered a similar fate.
Graham Kavanagh lifted his free-kick into the area and Lee, back in action after three months on the sidelines with a knee injury, made an immediate impact when he headed the ball wide of Murphy's left hand.
His second goal of the season looked to be good enough to earn Cardiff a point before one of Albion's substitutes helped turn the game in their favour.
Lloyd Dyer had only been on the pitch for a minute when he lifted the ball into the area.
Albion skipper Thomas Gaardsoe nodded the ball down and his header looked set to cross the line anyway before Hughes helped it home to seal a dramatic success.