Pakuranga has been held by Williamson since 1987, and he recorded a 12,867 vote majority at the last election.
Brown lives in Clendon Park with his wife, Rebecca, and has been on the Manurewa local board since 2013 when he was 22.
He stood for National in Manurewa in the 2014 election and collected 7636 votes, losing to Labour MP Louisa Wall's 14,038.
Brown said he plans to move into Pakuranga, and described himself as a centrist who is also a greenie.
"Pakuranga is an electorate which is 89 per cent surrounded by water, so that is an issue which is important to Pakuranga and an issue I am passionate about, I think we need to do more to care for our environment."
Brown, a Christian, said as well as playing the clarinet, he said another interest was gardening.
"Before the selection meeting last night we were out there picking some corn from the garden and cooking it for dinner which was nice. A good way to relax before a stressful evening."
Acknowledging he is a different character to the irreverent Williamson, Brown said he wanted to follow in his footsteps in being a strong advocate for Pakuranga, both within National and in Wellington.
Williamson will be the Consul General in Los Angeles after he announced in July he was not standing again this year.