| Last Updated: Thursday, 1 November 2007, 14:51 GMT |
Mugabe signs in a successor law
Robert Mugabe's choice would then be voted in by parliament which is dominated by his Zanu-PF party.
The constitutional amendment bill, which also allows presidential and parliamentary polls next March, had the backing of Zanu-PF and the opposition.
Mr Mugabe has said that he will seek another term in next year's elections.
Analysts say they expect Zanu-PF to dominate the joint elections in March 2008 and for Mr Mugabe to then put a hand-picked successor in place.