Municipal Affairs Minister Jim Watson will resign from cabinet and announce his candidacy for mayor on Tuesday, sources tell CTV Ottawa.

Watson, who represents Ottawa-West Nepean at the provincial level, will make the announcement at 10 a.m.

Watson previously served as Ottawa mayor from 1997-2000, prior to amalgamation. He also sat on city council from 1991-1997.

Two others have already signed up to fight for the city's top job. Coun. Alex Cullen and Rob Gauthier -- who's made several failed bids to run for city positions in the past-- both announced their candidacies last week.

Meanwhile, Mayor Larry O'Brien said Friday that he will wait until June before making a decision about seeking re-election. He said committing to a campaign now would be "ridiculously long".

O'Brien won the last municipal election with only three months of campaigning under his belt.

O'Brien previously told CTV Ottawa he planned to take the holidays to discuss his political future with his family, and would make an announcement in early January.

The nomination period runs from Jan. 4 to Sept. 10, and will elect one mayor, 23 city councillors, as well as school board trustees.

Residents will go to the polls on Oct. 25.