Around 100 senior local government figures attended the event, held at Painters' Hall in the City of London.
'Crime, education, employment, regeneration, the environment, all our crucial elements rely heavily on the effectiveness and innovation of local government,' Ms Armstrong said.
'The constitutional legitimacy of local government will be recognised for the first time in this country,' she added, referring to the party's commitment to sign the European Charter of Local Self-Government.
She dismissed CCT as 'an old-fashioned way of doing business'.
She admitted that, while in the Commons during the second reading of the Local Government and Rating Bill, she had wondered what it would be like to sit on the government benches.
Association of County Councils secretary Robin Wendt, responding on behalf of the guests, described Ms Armstrong's speech as amusing, thoughtful and challenging.
He described the Local Government Association as a 'solid, serious, desirable and practical step forward for the national representation of local government and the advocacy of local democracy'.
'It needs to use self-confidence, courage and controlled aggression. Local government is big business and we should punch our weight properly.'
He urged LGA members not to pursue diversity at the expense of unity.