Mr Seymour, 31, has been given the roles of Parliamentary Under Secretary to the Minister of Education and Parliamentary Under Secretary to the Minister of Regulatory Reform.
The roles were more junior than a minister or associate minister but were still executive positions and carried some responsibility.
National Party leader John Key made the announcement this afternoon as Act signed a confidence and supply agreement with the National-led government for the third consecutive term.
Mr Key said the two parties had worked constructively for six years and he looked forward to the relationship continuing with Act's new MP.
National agreed to work with Act on further developing and expanding the charter schools programme.
The programme, introduced in the two parties' 2011 confidence and supply agreement, has established nine privately-run schools so far.
The two parties also agreed to work on "reducing the regulatory burden" which "held New Zealand back", and to prioritise reform of the Resource Management Act.
In a press conference this afternoon, Mr Key said it was "highly likely" that Mr Seymour would be made a minister before the end of the term.
