The striker signed a four-year contract on Thursday evening after the Whites paid Swansea City an undisclosed fee thought to be in the region of £12m for the 24-year-old Dutchman.
And Leeds hope to wrap up three more deals before the deadline, with Bayer Leverkusen midfielder Nadiem Amiri thought to be closest to becoming their sixth acquisition of a window which has also brought Sam Bryan, Ethan Ampadu, Karl Darlow and loanee Joe Rodon.
The £24m sale of Tyler Adams to Bournemouth for £24m has allowed the Championship club to be more aggressive in their pursuit of targets after a summer which has seen seven players loaned out.
At least one centre-forward was a high priority after selling Rodrigo and losing Patrick Bamford and Mateo Joseph to injury.
Georginio Rutter is yet to adapt to English football, Willy Gnonto – who now looks likely to stay – works best from wide, and like Joseph, Joe Gelhardt and Sonny Perkins have potential, not proven pedigree.
In three years in south Wales Feyenoord and PSV Eindhoven academy product Piroe has shown his ability to perform at Championship level with 41 league goals in 91 matches.
Now the focus will turn to midfield, where greater depth is needed after Weston McKennie's unsuccessful loan ended, Adams was sold, Marc Roca loaned out and Adam Forshaw released.
Archie Gray and Ampadu have formed an impressive partnership but Leeds must not to ask too much of 17-year-old Gray in particular in his first season of senior football. The grandson of Leeds legend Frank can play further forward, whilst £7m signing Ampadu also provides cover at centre-back.
After conflicting reports earlier in the day, it was reported on Thursday afternoon that Leeds had agreed terms with 26-year-old Amiri.
A right-back is also a target with Luke Ayling exposed at times by manager Daniel Farke's fondness for pushing full-backs as high as possible, Sam Byram needed at left-back and doubts about West Ham United-linked Cody Drameh.
Understandably after his experience with Max Aarons, Farke was playing his cards close to his chest when asked about potential arrivals.
“If we are convinced about a player, his quality and personality, we try to bring him in as quickly as possible but I can't promise before the weekend something will happen,” he said.
But Piroe has arrived in time to feature at Ipswich Town on Saturday.