After Preki and Igor Simutenkov went down with long-term injuries before the beginning of the season, Arnaud was given a starting role in the Wizards' offense next to Josh Wolff.

Arnaud proved he deserved the opportunity from the outset, and went on to start all 30 of Kansas City's games, scoring nine goals and eight assists while leading the club to first place in the Western Conference.

On November 28, 2011, Arnaud was traded to new expansion team Montreal Impact for defender Seth Sinovic and allocation money.

[7] On July 13, 2020, Arnaud was named assistant coach for Austin FC, joining Josh Wolff's staff for the expansion club's inaugural campaign.

[1] Arnaud made his first appearance for the United States national team as a late substitute during the U.S.'s 4–2 friendly defeat against Brazil on September 9, 2007, at Soldier Field in Chicago.