The Robert Hickmott-trained seven-year-old was a head winner of the two-mile contest last year and has only raced twice since, winning a Listed event at Flemington in September before finishing fourth in a Group Three at the start of the month.
Almandin had been due to be ridden by three-times Melbourne Cup winner Damien Oliver, but he had his appeal against a 20-meeting suspension rejected at a hearing on Monday, allowing Dettori to step in for the ride.
Nick Williams, who owns Almandin in partnership with his father Lloyd, believes Dettori will match up well with the Monsun gelding.
He told Sky Sports Radio: "Frankie Dettori (will ride). It wasn't (always going to be Frankie). Dad had a couple of sleepless nights thinking about it. I guess he ultimately thought why not get a man who's won nine Group Ones for the season.
"I think he's won 11 in 17 in the last seven days. He's in fine form, he's going to the Breeders' Cup and he knows how to ride these staying horses.
"He hasn't won a Melbourne Cup yet, but I think the thing that probably swayed him (his father) was that Frankie openly said in an interview about three months ago in Europe that if he could achieve one more thing in racing, it would be to win the Melbourne Cup.
"You've got a man who's desperate to do it and dad, he and myself have had a huge association for probably 20 years. We know him well and we think he'll give him a good ride.
"I think he's a pretty straightforward sort of horse. You can see in his races he settles well, he goes when you want him to go and he comes back underneath you when you want him to do that as well.
"He's an older horse now, he's well experienced and I don't think Frankie will have any trouble with him.
"The truth of the matter is Frankie is great on these European-type stayers, he understands how to take them through the gears - they're a little different to the Australian horses
"We're thrilled to have him on the horse. We would have loved for Olly to have ridden him, but unfortunately circumstances have transpired and that's not going to occur, but we thought the next best for us was to get Frankie. "
Godolphin could still have two runners in the Melbourne Cup if last year's fourth Qewy can bounce back to his best in Wednesday's Bendigo Cup.
Hartnell is set to shoulder top weight at Flemington for Godolphin, but the Charlie Appleby-trained Qewy could also take his chance should he run well at Bendigo.
Appleby's travelling head foreman Chris Connett told www.racing.com: "It's all guns blazing for Bendigo and we'll see where we stand after that. Hopefully he goes and wins nicely at Bendigo and then that opens the door for Melbourne.
"If he doesn't, then that might close the door."
A total of 36 horses remain in contention for the Cup following the second acceptance stage on Monday.
Hugo Palmer's Wall Of Fire has moved to 24th in the order with only the winner of Saturday's Lexus Stakes able to push him out of the final field if there are no further withdrawals by Saturday evening. Willie Mullins' Thomas Hobson is now 26th.