Japanese insurer Nippon Life has agreed to purchase a controlling stake in rival Mitsui Life Insurance.
Under the deal Nippon will buy an 85% stake in Mitsui for an undisclosed sum.
According to Nippon, the two firms will retain their separate identities and purpose of the takeover is to "expedite growth of the domestic life insurance market".
Nippon Life said the firms would not consolidate their sales offices and Mitsui Life employees would remain employed, with no adverse changes to employment terms.
Established in 1889, Nippon Life has more than 70,000 employees and as of 2014 it had about 62.2trn yen (£335bn) worth of assets and 3.32trn yen (£17.9bn) of premiums in force. Mitsui Life has more than 10,000 staff and reported 7.4trn yen (£39.9bn) of assets and 510 billion yen (£2.7bn) of premiums in force in 2014.
Fitch said the transaction would increase Nippon Life's market share in the Japanese life insurance sector to 20.8% from 18.3%. Standard & Poor’s said the deal would boost Mitsui's credit profile because it would receive group support from Nippon.
Both insurers are expected to sign a definitive agreement in late October or early November. The deal is expected to be completed in March 2016, subject to regulatory and shareholder approval.