Kornblau will fill in the position left vacant by Gary Ginsberg, who resigned in December last year, according to media reports.
Ginsberg was on an indefinite leave of absence since last January to advise Michael Bloomberg's U.S. presidential campaign, Reuters reported, citing people familiar with the matter.
Ginsberg has also served as a top adviser to Rupert Murdoch and in former U.S. President Bill Clinton's administration.
Kornblau will join Softbank on Aug. 16 from the NBCUniversal News Group, where he is executive vice president of communications. He will be based in SoftBank's New York office and report to Chief Executive Officer Masayoshi Son and Marcelo Claure, CEO of SoftBank Group International.
Before NBCUniversal, Kornblau was managing director of corporate communications for JPMorgan Chase and served as spokesperson for Ambassador Susan Rice at the United States Mission to the United Nations.
Kornblau has also held senior communications roles on two U.S. presidential campaigns, on Capitol Hill and on U.S. House and Senate campaigns.
(Reporting by Noor Zainab Hussain in Bengaluru; Editing by Shinjini Ganguli)