The Everton defender, who is now 27, was one of 11 players who made their way to Albion this summer.
Holgate was expected to go to Sheffield Wednesday on loan, but then West Brom came in for him.
Per the Express and Star, he said: "I’m over the moon to be back. As soon as I heard there could be a chance of coming here I was pushing it and it was a no-brainer.
“I’ve had a strong feeling for the club ever since I joined a few years ago. I felt so at home the first time I was here and I’ve always kept a look out for the results.
“I’ve been to the odd game and I’ve kept in contact with a few of the boys.
“The move came through quite late and it was pretty hectic. I couldn’t have asked for a better place to come. If I could’ve picked anywhere to come it would’ve been here, so I’m more than happy to have waited to get the club that means something to me.
“I’ve got an affinity with the fans. We fell a little bit short the last time I was here, losing on penalties in the Play-Offs, but ever since then, when I’ve played against Albion the fans have been great with me.
“To get a good reception again on Saturday before the game against Swansea was great, but I’ve got to repay that this season and show why they’ve stuck with me.”