“I declare myself to have full responsibility for taking the political initiative” to hold the non-binding vote in defiance of the Spanish authorities, he told a news conference.
He earlier went before a judge charged with civil disobedience and misuse of public funds for staging the vote on November 9th, 2014.
Thousands of cheering separatists rallied outside the court in his support during his hearing on Thursday morning.
Mas's allies have branded the case against him politically motivated and accuse Spanish authorities of going after him to disrupt his drive for the rich northeastern region to secede.
The Catalan independence movement has raised political tensions in Spain as it recovers from several years of recession and prepares for a general election on December 20th.
The Spanish government says holding an independence vote is against the constitution since all Spanish people have the right to decide on matters of sovereignty.
“I am responsible for having listened to hundreds of thousands of people who peacefully filled the streets and squares of Catalonia” in demonstrations for independence over recent years, Mas said.
Rallies outside court
The 59-year-old Mas earlier waved to a crowd outside the courthouse before and after the preliminary hearing in a judicial process that could see him barred from public office.
Local police said some 3,000 people joined the demonstration in his support.
“We are all Mas,” yelled the crowd.
— Catalan Government (@catalangov) October 15, 2015
In a sign of the tensions over the statehood drive, the court service earlier complained that such demonstrations near the tribunal were an “attack on judicial independence”.
Mas and his two codefendants deny the charges.
He said he told the court the vote was organised by volunteers and he gave no “orders or instructions” in its organisation.
Last year the Spanish government went to court to block Mas's plan for a full referendum, like Scotland's independence vote in September 2014.
The Constitutional Court, whose judges are mostly conservative and appointed by Spanish leaders, upheld its complaint.
Mas instead staged the November vote as a non-binding symbolic ballot.
About 2.3 million of Catalonia's 7.5 million inhabitants took part and nearly 1.9 million voted in favour of independence.
“A democratic success should never end up in the law courts,” he added. “This is a political case and should have a political solution.”
The hearing coincides with a sensitive date in Catalan history: the 75th anniversary of the execution of Catalan nationalist leader Lluis Companys by firing squad under Francisco Franco's dictatorship.
Lluis Companys, leader of Catalonia during the Spanish Civil War. Wikimedia
Before his hearing, Mas laid flowers at a ceremony to commemorate the death of Companys, who in 1934 declared a short-lived Catalan state. Mas's supporters bitterly criticised the choice of date for the hearing.
Catalans' long-standing demands for greater autonomy have intensified over recent years as Madrid has resisted their bids for reform, and have surged in the recent economic crisis.
Deepening the conflict with Madrid, Mas teamed up with other separatists in a joint list in the September 27th Catalan regional election, making it a de facto vote on secession.
The alliance won enough seats to control the Catalan parliament if it teams up with the far-left separatist group CUP.
Mas's alliance had vowed to declare independence for Catalonia by 2017 if it won, but it must first reach an agreement with the CUP.