Darling spoke at the launch of the Better Together campaign in Edinburgh, two years before voters would decide whether or not Scotland would remain a part of the United Kingdom, The Daily Telegraph reported.
"Chairing this campaign is one of the most important things I have ever done in politics," he said. "The decision we make is the most important we will make in our lifetime. Those of us who believe that it is best for Scotland to be part of the U.K., from whatever political views, have a duty now to work in harmony to argue for the better, stronger choice."
The vote on independence is a "chance to reaffirm Scottish values and our expression of them in our partnership with our neighbors," Darling said.
Meanwhile, Scottish National Party leader First Minister Alex Salmond responded to Darling's comments in a release.
"Alistair Darling's use of smoke and mirrors during his speech exposes a campaign mired in negativity. His threadbare case against independence has been exposed by the weakness of his arguments, and his presentation suffered from three devastating failures," Salmond said.
"Firstly, he claimed that the union was a 'celebration' of Scottish values, on the very day that the prime minister of that political union is proposing to eliminate housing benefit for young Scots," he said, and went on to say, "Secondly, the anti-independence campaign's claim to be making a positive case has been exposed as a fraud. Alistair Darling's presentation was littered with words such as 'borders', 'division' and 'upheaval' -- expressing arguments better suited to the 18th century than to the 21st."
"Thirdly, Alistair Darling said not a single word about the anti-independence campaign's alternative vision of more powers for the Scottish Parliament," Darling said. "That is because -- at heart -- this is a Tory-led campaign, which is intent on conceding nothing to the people of Scotland, and hiding behind its refusal to spell out an alternative policy before the referendum. Urging people to vote no with only vague Tory promises of something else will only encourage more people to vote Yes to an independent Scotland."