From 2005 to 2010 she was head of Field Court Chambers and was Chair of the Family Law Bar Association in 2008 and 2009. In 2010 she was appointed to be a High Court Judge.
In 2011 the President of the Family Division appointed her a Family Division Liaison Judge on the South Eastern Circuit with responsibility for Kent, Surrey and Sussex and in 2017 for London and Thames Valley.
Since 2018 she has chaired the Family Procedure Rules Committee and the Family Justice Council and is the lead judge in relation to applications under the HFEA 2008.
Mrs Justice Theis was appointed as the Senior Family Liaison Judge for a four-year period from October 2018. This is in addition to her role as the Family Division Liaison Judge for London.