Aon Sees $30 Billion Takeover as Answer to Age of Volatility

Aon Plc agreed to buy Willis Towers Watson Plc in an almost $30 billion transaction, creating the world’s biggest insurance brokerage and adding a raft of experts on everything from climate change to cybersecurity.

The all-stock deal, the largest ever for the industry, will combine the second- and third-largest brokers and comes almost exactly a year after previous talks between the two companies broke down.

Insurance brokers have been seeking ways to scale up their businesses advising corporate clients on new and evolving threats. Marsh & McLennan Cos., which will be supplanted as the biggest brokerage when Aon’s deal is ...