Terrell was Board Certified in Estate Planning and Probate Law in December, 1999 by the Texas Board of Legal Specialization. Terrell's major role in the firm is to concentrate on the more technical aspects of estate planning. Terrell was admitted to the State Bar of Texas in 1982 and belongs to its Real Estate, Probate and Trust Law Section. Terrell is also a member of the Dallas Bar Association and its Probate, Trusts and Estates Section.

Terrell was born in 1957 in Liberty, Texas, where he lived until attending the University of Texas at Austin, where he received a B.B.A. in accounting, with highest honors, in 1979. He received his J.D. from Southern Methodist University School of Law in 1982.

Having taken a break from the law practice to be a missionary with Operation Mobilization from 1987-1994, Terrell lived and worked throughout Eastern Europe and in Austria, and speaks German fluently. He also taught legal English to the Counsel for the Provincial Government of Lower Austria during his time in Europe.

When not practicing law, Terrell spends time with his wife and daughter, reads (nonlegal materials), and plays electric guitar.