Gareth Southgate's side have made an unexpected charge to the semi-finals of the tournament, helped by a number of upsets along the way which have eliminated some of the pre-tournament favourites.
England's most recent appearance in a World Cup semi-final saw them lose on penalties to West Germany in 1990, but Walker believes that 2018 is their best chance since they lifted the trophy on home soil in 1966.
"It's a great opportunity. I think we all know that. I think it's the best opportunity that England's ever had [since 1966], and probably might ever have because no disrespect to Croatia but the other side of the group was a lot more difficult. They have got some fantastic players. I've played with Luka [Modric] and for me he is one of the best midfielders in the world by far. But we have to just adapt ourselves to their game plan, but also they have to worry about us," he told IRN.
"We've played well, we've played well in the games. I think we've shown immense character. The goal going in against Colombia and us digging ourselves out and stepping up for the penalties and the five penalty-takers taking them, full credit to them. So we have shown character, we've shown belief and I think that's what is going to get us over the line in this game.
"It's special. It really is. That's the only word I can describe it because we're all a family. I said at the start of this that over this summer, this is our family. You obviously have got your family at home and the kids that you need to keep in touch with, keep checking in or the missus might go mad. But this is our family now.
"[We hoped we would have] a long month together, which we have done. And we've completed a World Cup. We have completed it. If we get to the final or if we don't get to the final then we're one day short, you know it has been an absolute pleasure of an experience to share not just with the players but the staff, even the media staff and you guys as well. Thank you for coming on our ride with us."
Should England beat Croatia then they would face either France or Belgium in the final on July 15.