Leah went in to Saturday night's live final as the hot tip to win, but was beaten in the final public vote by Andrea Begley.
But Will - who previously criticsed the show's record label for moving too slow last year - is keen to start working with Leah right away.
"Its time to focus and build...let's go @leahmcfallmusic...I'm so pumped....me and leah will start next week...#newORIGINALsongs," he wrote on his Twitter page.
Will continued: "As a matter of fact...let's start in nyc next week...somebody wake up the wizards...let's make magic @leahmcfallmusic
"Let's have a some new songs finished before #wirelessFESTIVAL #boom...let's go!!!"
Meanwhile, Will still seemed pretty annoyed that Andrea had beaten Leah in the final.
He tweeted somewhat begrudgingly: "Andrea is amazing...#dontGETmeWRONG...but we know who has the incredible #voice"
And the Black Eyed Peas star retweeted another user who wrote: "Andrea won, yet Leah has 4 top 30 songs in iTunes, and a top 10 UK single @iamwill #whostherealwinner #winnersmakehits"
Leah herself was still clearly on a high from the series however, and gushed: "Best time ever at @BBCTheVoiceUK over the past few months. Congrats to my girl @ABegleymusic !!! Insane enchanting vocal!! So proud!"