The Securities and Exchange Commission announced Monday that Daniel M. Gallagher has been sworn into office as an SEC commissioner and begun his tenure.

Gallagher was administered the oath of federal office on Friday evening by U.S. District Judge J. Frederick Motz, and officially assumed his new role at the Securities and Exchange Commission on Monday.

Appointed by President Barack Obama on Oct. 24,Gallagher returns to the agency where he worked for four years as a counsel to prior commissioners and as deputy director of the Division of Trading and Markets.

“I’m looking forward to working together with Dan on the complex issues facing our markets,” said SEC Chairman Mary Schapiro, in a statement.

Gallagher’s first tenure at the SEC began in January 2006, serving as a counsel to SEC Commissioner Paul S. Atkins and later as a counsel to SEC Chairman Christopher Cox. He worked primarily on major matters before the commission involving the Division of Trading and Markets and the Division of Enforcement.

After joining the Division of Trading and Markets as a deputy director in 2008, the SEC says that he played a key role in the SEC’s response to the financial crisis and other key issues before the commission at the time, including credit rating agencies and credit default swaps. He served as co-acting director of the Trading and Markets Division from April 2009 to January 2010, after which he left the agency to become a partner in the Washington, D.C., office of WilmerHale.

Prior to his initial SEC service as a staff member, Gallagher was the general counsel and senior vice president of Fiserv Securities Inc., where he was responsible for managing all of the firm’s legal and regulatory matters. Gallagher began his career in private practice, advising clients on broker-dealer regulatory issues, and representing clients in SEC and SRO enforcement proceedings.

Gallagher earned his law degree, magna cum laude, from the Catholic University of America, where he was a member of the law review. He graduated from Georgetown University with a Bachelor of Arts degree in English.