Hovannisian lost to incumbent Armenian President Serzh Sargsyan, who took 58.6 percent of the vote during a Feb. 18 contest.
Hovannisian said he was going on a hunger strike, calling on Sargsyan to step aside before his April 9 swearing-in ceremony, reports Russia's state-owned news agency RIA Novosti.
In 2008, opposition leaders in Armenia called for protests in Yerevan citing irregularities in the presidential elections. An international election observation mission expressed similar concerns over the February vote, saying that while the election was calm and orderly, there were signs of interference at the polls, primarily by supporters of Sargsyan.
Hovannisian's campaign last week said it filed an appeal in court challenging the results of last month's election.