 On 8 July 1999, Theobald signed a three-year contract with newly-promoted Second Division club Brentford on a free transfer.He was utilised as cover for injuries and had a run in the team as a stand-in right back for the injured Danny Boxall during the 1999–00 season and in central defence for Scott Marshall during 2000–01.Theobald was named in the starting lineup for the 2001 Football League Trophy Final and received a runners-up medal.