He spent six seasons playing for Spartak Moscow in the Russian Premier League. Previously he played for Tiligul Tiraspol in Moldovan championship, having joined them in the 1999 pre-season. His contract with Spartak ended in 2009.
An Odessa native, Serghei Covalciuc previously had Moldovan and Transnistrian (de facto nation) citizenships, but, in 2007, he renounced them to receive Romanian citizenship and be able to play more often for Spartak.
On February 23, 2010, Tom Tomsk signed Covalciuc on a free transfer and on a two-year deal. After playing for half-a-season for Football Club Zhemchuzhina-Sochi in the Russian First Division in 2011, Covalciuc transferred to his home-city team Chornomorets Odessa in the Ukrainian Premier League on August 29, 2011.
Covalciuc made 41 appearances for the Moldovan senior squad, including three games in Union of European Football Associations Euro 2008 qualifying. He played his last official match against Turkey on October 11, 2006 before denaturalization of his Moldovan nationality.
In 2012, he was recalled to the national team, making a further seven appearances.