He played in Major League Baseball (MLB) for the Boston Red Sox, Milwaukee Brewers, Oakland Athletics, Kansas City Royals, Cleveland Indians, St. Louis Cardinals, and Toronto Blue Jays.

He played in the 2006 All-Star Futures Game for Team World[3] and was named number 48 in the 2006 Minor League News FAB50 List.

[4] On September 5, 2006, he was traded to the Boston Red Sox to complete an August 31 deal for David Wells and was immediately added to the team's 40-man roster.

[5][6] He was assigned to the Red Sox Double A franchise, the Portland Sea Dogs, who had just begun their Eastern League playoff run.

[9] Then, after Pawtucket was eliminated from the International League playoffs, he was called up from Pawtucket to MLB on September 8, 2008, [10] and on September 13, 2008, made his MLB debut in the sixth inning of a game against the Toronto Blue Jays and scored the only run for the Red Sox that game.

After Wakefield went on the disabled list after the All-Star break, Kottaras followed suit with a lower back strain.

Kottaras hit his first MLB home run on July 3, 2009, against the Seattle Mariners' Mark Lowe in the bottom of the 11th.

[19] Just a day after agreeing to that contract, Kottaras was designated for assignment to clear a roster spot for the newly acquired John Jaso.

[23] On December 2, Kottaras signed a one-year deal with the Cubs for $1.075 million, avoiding arbitration.

[33] Kottaras made his debut for the Blue Jays on September 17, grounding out in his only at-bat against the Baltimore Orioles.

Kottaras went 0–4 as a member of the Blue Jays, and finished the season with a .233 average, three home runs, and 5 RBI.

[35] On December 18, 2014, Kottaras signed a minor league contract with the Chicago White Sox that included an invitation to spring training.

[45] On July 21, 2004, Kottaras had three hits helping Greece to come from behind to defeat Italy 11–7 for the team's first and only win in the tournament.