The Melchizedek - equivalent to 40 standard bottles - stands four feet tall and is worth £4,000.
The huge bottle of Drappier was specially ordered from the shop on Portland Street by a Southport businessman who collects champagne, but it will be on display for another week.
The same man bought the second-largest size - a 36-bottle Primat - from the store several years ago.
“This is the largest mass-produced bottle in the world, but they only make around 20 a year,” Portland Wines owner Dave Smith said.
“They are made to order and it has taken about 12 weeks for it to arrive. It is exciting for all of us to have it on display in the shop.”