The Northern Ireland U17 international defender turned 17 last week and has now penned pro terms with the Irons. Leacock joined the Hammers in July from Linfield.
Leacock told whufc.com: “It's a great feeling for me and my family. It's every boy's dream to get his first professional contract, and it's what I've been working towards since the age of seven.
“I’ve been here for around seven weeks now, and the boys and staff have been really good with me. It's been a really easy transition because they've helped me on the pitch a lot.
“It's been a big change in my life because, in Northern Ireland at Linfield, I was only training around two nights a week. Over here, you're in every day and performing at a high standard, but I think I've adapted well.
“I started at my local club in Magherafelt Sky Blues, and we had a really good team. Then at the age of about ten, I made the move to Linfield. I was at Linfield for about six years and was lucky enough to make my first-team debut against Larne FC in April.”