Henry settled affairs ten minutes into the second half with a cool piece of finishing. The Wolves skipper drilled home a low drive from fully 25 yards after Freddy Eastwood had played a clearance from Wayne Hennessey into his path.
The win extended promotion-chasing Wolves' impressive run to just one defeat in 12 games.
But it was tough on struggling Preston who did more than enough to take at least a point from the game after a battling display that was again inspired by captain Paul McKenna.
Preston have now lost all three games since Irvine replaced Paul Simpson and it must be hard for them to accept that 12 months ago they were sitting at the top of the table.
Wolves started at a frantic pace and should really have been in control of affairs inside the first five minutes.
But Eastwood was out of luck - seeing Yawl Mawene block his close-range drive and then, 60 seconds later, crashing a Stephen Ward cross against the post with Stephen Elliott firing the rebound into the side-netting. Eastwood was then denied by a stunning save from Andy Lonergan.
Hennessey's quick free-kick, after Liam Chilvers had a goal disallowed for offside, caught out Preston and released Elliott.
The Irishman unselfishly crossed for Eastwood but Lonergan spread himself to beat away his shot.
Having successfully ridden their luck, Preston forced their way back into the game and were unfortunate not to break the deadlock themselves before half-time.
Callum Davidson sliced wide when he only had Hennessey to beat in the 15th minute and then McKenna shot weakly at the Wales international when well-placed on the half-hour.
McKenna then wasted another good chance when he fired wide just five minutes before Henry broke the deadlock.
To their credit, Preston kept battling but Hennessey held on to Simon Whaley's free-kick and then tipped away Neil Mellor's cross-shot.