Hertz has bought rival Dollar Thrifty for approximately $2.3bn, which is about twice what it offered two years ago.
Earlier attempts by Hertz to buy the budget car rental giant were blocked by regulators, but it will appease them this time round by selling its own budget brand, Advantage, to Franchise Services of North America and Macquarie Capital.
The merger of the Hertz and Dollar Thrifty brands will save about $160m a year and Hertz said it would enable it to expand.
Avis Budget Group has also previously tried to buy Dollar Thrifty, but it did not enter a bidding war this time around, said commentators.
The sale by Dollar will leave just three major players – Hertz, Avis Budget and Enterprise – controlling the majority of the US car rental market.