The Condor Ferries service arrived from Jersey at about 07:00 GMT, but a fault with the internal ramp meant cars on the upper deck were unable to get off.
Condor said 110 people and 44 vehicles had been stuck, but said they had all disembarked shortly before 20:00 GMT.
Passenger Kit Ashton, from Jersey, said a crane had been needed to help cars off, describing it as "a nightmare".
Condor said the fault meant it had not been possible to lower the ramp from the upper vehicle deck of its Commodore Clipper ferry.
The firm said foot passengers had been able to disembark upon arrival, but engineers had to work throughout the day to lower the ramp. They required a specialist crane to help, it said in a statement.
Mr Ashton was one of a number of passengers who had already been moved to the Clipper ferry, having originally been booked on Condor's Liberation ferry.
The Liberation developed two technical faults on Friday and its services between the Channel Islands and Poole had been cancelled.
Mr Ashton said: "We got off just before 20:00, so it was basically 26 hours since I checked in. It has been an absolute nightmare.
"I should have been in Poole at 23:00 last night, but here I am in Portsmouth 26 hours later," he added.
By Paul Clifton, BBC South's transport correspondent
This is the latest in a string of technical failures to hit Condor Ferries in the past year.
The fast ferry Liberation has endured breakdowns and incidents and now the normally reliable Commodore Clipper is adding to the company's difficulties.
It all means that Condor is hitting the headlines for the wrong reasons more frequently than other ferry operators.
Mr Ashton, who was travelling to Exeter, said several animals were also on board the vessel, including several dogs and a horse.
He said passengers had to wait while the crane arrived to help support the ramp. He called on Condor to improve services to the Channel Islands.
Condor's executive chairman, Russell Kew, said: "I'd like to apologise to all those customers who have been inconvenienced over the last 24 hours, and to thank them for their understanding and patience."
Dozens of vehicles were stuck on a ferry in Portsmouth for more than 12 hours after a ramp to disembark failed.