Mr Barclay (24) has been selected to replace Deputy Prime Minister Bill English, who has announced he will retire as an electorate MP at the September election and become a list-only MP.
Regional chairwoman Ele Ludemann said Mr Barclay had ''big shoes to fill'' after Mr English's 24-year tenure.
''I know Todd will work hard to earn the trust of Clutha-Southland communities,'' Mrs Ludemann said.
Mr Barclay was raised in Dipton and Gore, attending Gore High School before gaining a bachelor of commerce degree in commercial law at Victoria University, in Wellington.
He previously worked for Mr English, cabinet ministers Hekia Parata and Gerry Brownlee and for the Philip Morris tobacco company.