Plaid Cymru's annual conference has explicitly committed the party to achieving independence for Wales.
A motion pledging the party to securing "independence for Wales in Europe" was backed overwhelmingly by delegates in Llandudno.
Plaid's constitution previously stated it aimed for "full national status for Wales within the European Union".
Welsh Secretary Cheryl Gillan accused the party of an "isolationist agenda".
The use of the term independence has been a bone of contention in Plaid Cymru for decades.
Former Plaid Cymru leader Dafydd Wigley famously declared in 1999 that the party had "never ever" advocated independence, and follows the election successes of the Scottish National Party (SNP) in Scotland.
Throughout this conference many senior party figures have drawn parallels with the SNP's pursuit of independence and now believe that this is a path that Plaid should now follow.
It has, however, always been a long-term aim of many party members.
The change comes at a time when Plaid Cymru is engaged in a wide ranging review, after disappointing assembly election results and Ieuan Wyn Jones' decision to stand down as leader in March.
Conference delegate Marcus Warner said: "On the surface the motion may seem a bit trite, maybe a technicality, but I don't agree.
"The lifeblood of our renewal as a party and as a nation must be a crystal clear commitment to independence."
In response, Conservative Welsh Secretary Ms Gillan said: "Their (Plaid's) aim is to cut Wales off from the rest of the United Kingdom when what is vital for economic growth, investment and prosperity is the inter-dependence between the four nations of the Union," she said.
Earlier, a motion that would have committed Plaid to opposing the building of a replacement for the nuclear power station at Wylfa on Anglesey was narrowly defeated by 42 votes to 41.
A contender for the leadership of Plaid Cymru urged the party's annual conference to "reach out" to a wider section of the population of Wales.
Ceredigion AM Elin Jones told delegates in Llandudno it is time to "open our doors to more people and challenge our comfort zones".
Ms Jones said that the party had "stagnated of late" and that they had failed to motivate themselves.
Ieuan Wyn Jones is stepping down as party leader next year.
Ms Jones told delegates that Wales "needs to be more than somebody else's afterthought".
In a speech containing numerous references to the word "independence", Ms Jones called for a "constitutional and fiscal debate within the four countries of the UK" and "between the four countries" because "the constitutional imbalance" of the UK was "unsustainable".
A possible yes vote for Scottish independence, she said, would change the UK "irrevocably".
'Not one glorious step'
But Ms Jones, the party's communications director, said it was the people of Wales who would decide Wales' constitutional future.
"It is not one glorious step for independence - otherwise it would be a hell of a big step," she said.
"We can't just jump to the final chapter because the people of Wales still want to read the book."
Dwyfor Meirionnydd AM and former party president Dafydd Elis-Thomas has also confirmed his intention to run for the Plaid leadership when the contest opens early next year.