His comment came after Finland's leaders formally expressed their support for NATO membership.
"First of all, that changes the security situation in the Baltic region dramatically," Landsbergis told reporters. "It is a huge strengthening of the Alliance and a huge strengthening of the Baltic region."
"Finland is a very strong country militarily, an experienced country with a navy, with air defense elements," he said. "Its recent acquisitions of F-35s from the US are a huge reinforcement for the Alliance."
Earlier on Thursday, President Sauli Niinisto and Prime Minister Sanna Marin said in a joint statement that "NATO membership would strengthen Finland's security".
"As a member of NATO, Finland would strengthen the entire defense alliance. Finland must apply for NATO membership without delay. We hope that the national steps still needed to make this decision will be taken rapidly within the next few days."
Finland's political and public opinion has swung dramatically in favor of NATO membership after Russia invaded Ukraine on February 24.
Neighboring Sweden is also considering joining the Alliance.