McDonald, 31, has signed a one-year deal with the Perth club, who are under the tutelage of new boss Tommy Wright following the departure of Steve Lomas to Millwall.
The midfielder last played in Scotland with Hamilton before leaving the Lanarkshire club in 2010 to join Morecambe.
McDonald previously played for Aberdeen, Oldham and Kilmarnock and was capped by Scotland B in 2005, scoring in a 2-0 win over Poland.
Miller joined St Johnstone from Ross County last summer while Wright moved in 2011 from Kilmarnock.
- Sports & Recreation
- Steve Lomas