MPO took the decision at its conference in Eastbourne last week.
Delegates believed TUC membership would improve MPO's relations with local authorities and other unions, and give it access to the TUC's research and training facilities.
The proposal to start negotiations was passed by a two-to-one majority.
'There has been a groundswell for some time that we should be looking at the TUC. There were concerns that a union for senior local government officers should not be politically affiliated, but the majority now see the TUC and the Labour Party as very separate,' he said.
He felt Labour leader Tony Blair's moves to make a clearer distinction between the party and the unions had been partly responsible for the widespread support for affiliation. He stressed the affiliation move did not signify a move to the left in the union. He did not expect TUC membership to mean the union would be given a negotiating role in the white-collar pay negotiations.
Mr Corless was unsure if TUC membership would cause any MPO members to quit.
There is no guarantee the TUC will accept MPO's membership application.
As part of TUC moves to rationalise the trade union movement it will examine whether MPO should merge with an existing TUC member which already services the same types of staff.
The obvious candidate would be Unison, which disagrees with MPO on many issues. MPO claimed this year's pay deal helped the lower paid at the expense of higher-paid staff.
And if MPO overcomes this hurdle it still has to have its application approved by the TUC general council.
MPO has been notably uncomplimentary about Unison, and if Unison now objected to MPO being allowed to join the TUC the general council would throw the application out.
Unison would not comment on the stance it was likely to take.
MPO was formed in 1986 and claims a membership of 12,000 senior managers and chief officers in local government, the health service and the water industry.