"I decided to run for the presidency of the Republic of Lithuania," he said at an event in Kaunas.
In his speech outside Kaunas Castle, the 53-year-old diplomat vowed to tackle social inequalities and to seek that Lithuania's economic growth accelerate to at least 6 percent annually, twice as fast as the current rate.
"It's a shame to hear about a Lithuania of two and a half cities when we have every potential to create a Lithuania of ten strong counties," Ušackas said as he presented his election program, entitled "A Winning Lithuania".
The former foreign minister said that Lithuania has lost its strategic direction and hope after joining the EU and NATO.
"We can, all together, create a breakthrough if we have a direction, hope, faith and if we work together," he said.
The diplomat also vowed to further strengthen Lithuania's defense and seek NATO's permanent presence in the country.
Usackas said that his lengthy experience as a diplomat will be helpful if he is elected president.
He added that he is well aware of Lithuania's domestic problems, too, as he has visited many cities and towns in the past year.
The 53-year-old held the post of Lithuania's foreign minister in 2008 to 2010. He has served as the country's ambassador to the United States, Britain, Afghanistan and Russia.
Both Ušackas and Nausėda will also have to decide by the end of this month whether to contest in the conservative Homeland Union–Lithuanian Christian Democrats' primaries for next May's presidential election.
In his speech, Ušackas thanked the Homeland Union's branches that nominated him as a candidate, but added that he will be "the ambassador of all people of Lithuania, regardless of their party affiliation, political views, religion or nationality".