Undrafted by an NBA franchise, Singleton began his professional career in Italy playing with the Sicc Cucine Jesi (Lega2) during the 2003–04 season, averaging 20.8 points and 12 rebounds per game.

He averaged 11.5 points, 8.6 rebounds and two steals in 46 games during the 2004–05 season, helping his team reach the Italian SerieA League Finals.

Achieving success in Europe again Singleton returned for his second opportunity in the NBA as several teams took notice of his marked improvement.

On February 13, 2010, Singleton was traded from the Dallas Mavericks to the Washington Wizards along with Drew Gooden, Josh Howard and Quinton Ross for Caron Butler, Brendan Haywood, and DeShawn Stevenson.

[1] On September 6, 2010, The Washington Post reported that Singleton had rejected a contract offer from the Wizards and signed with the Xinjiang Flying Tigers of the Chinese Basketball Association in which he helped lead the team to the CBA finals.

[8] He left Kiryat Gat after appearing in eight games, and on December 20, 2016, he signed with Seoul SK Knights of the Korean Basketball League.