David Simison was admitted to the Maryland Bar in 1979. He was later admitted to the Bar in Washington D.C. and West Virginia. Even before law school he searched real estate titles in Anne Arundel County, Baltimore City and Denver, Colorado. After clerking for a Judge in the Anne Arundel County Circuit Court, he started practice in Severna Park, Maryland. He had offices later in Arnold, Millersville and Annapolis. He has been in sole practice since 1986. He has represented builders, developers, homebuyers and landowners. He has been mediating since 1998 for the Courts of Anne Arundel, Howard, Queen Annes and Caroline Counties.
He was active in the Anne Arundel County Bar Association for many years and served in various positions as an officer, on the Board of Trustees and as President. He was President of the Anne Arundel Bar Foundation helping to found the Anne Arundel CASA (Court Appointed Special Advocates). He served on the Board of Governors of the Maryland State Bar Association and is a member of the Maryland Bar Foundation. Most recently he chaired the Alternative Dispute Resolution (Mediation) Section of the Maryland Bar Association.