In a statement issued by his spokesman, Adamkus, 77, said he made his decision based on a desire to act "in the interest of Lithuania" and pledged to remain a nonpartisan candidate.
In an interview granted to the news agency ELTA months earlier, Adamkus shocked onlookers when he pledged he would not "declare my own candidacy."
However, shortly after the April 6 removal of Paksas, Adamkus, who served as president from 1998 until 2003, stated he would "have no choice but to run" if Paksas entered the race as well.
Paksas, who defeated Adamkus in January 2003 to become president, declared his candidacy on April 19 despite having just been impeached.
Adamkus will join an ever-widening field of candidates that by Monday included six other names, including fellow center-right candidate Petras Austrevicius, Lithuania's former chief EU negotiator who joined the race on Friday.
The first round of presidential elections will be held on June 13.