The Scotland Act 1998 (Transitory and Transitional Provisions)(Standing Orders and Parliamentary Publications) Order 1999

Rule 2.4 First meeting following general election

4.  If the person holding the office of Presiding Officer as mentioned in section 19(2) is not a member of the Parliament, that meeting shall be chaired by that person but only until a new Presiding Officer is elected. Thereafter it shall be chaired by the elected Presiding Officer.