Grosvenor managing director Allan Yeo said the deal will put the combined entity in a strong position to become a default provider.
The default KiwiSaver system, in which investors who do not select a KiwiSaver provider when they enrol are put with one of five default providers, is up for review next year.
"Depending on what the Government decides to do, if they decide to re-tender the scheme, we'd like to think we'd stand a reasonable chance of being selected given we're essentially only about 600 members short of being number six [in the market]," Yeo said.
The Fidelity scheme will be managed separately by Grosvenor and remain as a distinct entity to begin with.
But Yeo said he would like to discuss the merger with the Financial Markets Authority.
Fidelity will continue to work with Grosvenor on investment issues when the deal is done, said Fidelity Life chief executive Milton Jennings.
Yesterday's announcement follows Fisher Funds' acquisition of Tower's KiwiSaver scheme earlier this year.
That purchase was the fourth KiwiSaver provider bought by Fisher Funds in the past three years.