Airbnb announced Thursday that it will acquire hotel booking site HotelTonight as it builds an expansion narrative ahead of an eventual initial public offering.

In recent years, Airbnb has expanded its offerings to include boutique hotels and luxury properties as it faces increasing competition from online travel agencies and hotels. It now bills itself as an "end-to-end travel platform."

HotelTonight will help the start-up accelerate its push into more traditional hotel listings and bring more inventory to the platform.

The company did not disclose the price or when the deal is expected to close. HotelTonight was last valued at $463 million in the private market.

In a press release, Airbnb said that guests are using the platform for business and last-minute travel, leading to same-day bookings doubling year over year.

The two platforms will continue to operate as separate entities, but Airbnb said that some HotelTonight listings will become part of the larger platform in the future.

Sam Shank, co-founder and CEO of HotelTonight, said in a statement that the merger will bring "more choices and the world's best boutique and independent hotels a genuine partner to connect them with those guests."

It could also help both companies compete better against the major traditional hotel chains who have gone on the offensive to protect themselves from the disruption Airbnb has created in their sector.

A source close to the deal told CNBC that Airbnb's co-founder and CEO, Brian Chesky, and Shank have been friends for years and they both felt like "Davids going against the Goliaths of the hotel industry."

To research the deal, Chesky spent two weeks booking and living in different HotelTonight properties.

Airbnb is among the class of aging unicorns, including Uber and Lyft, that are starting to go public this year at multibillion-dollar valuations. Airbnb has raised more than $4 billion in capital and was last valued at $31 billion.

To justify a public market debut at that level or higher, Airbnb is moving beyond its core business of short-term home rentals.

Chesky has said that the company would be ready to go public this year, but never committed to doing so. A source close to the matter told CNBC it's unlikely to be this year.

Airbnb posted its second straight year of profitability in 2018, setting it apart from the other unicorns eyeing IPOs like Uber and Lyft that are still losing hundreds of millions of dollars each year.

Earlier this year, The Wall Street Journal reported that Airbnb was in talks to acquire HotelTonight, but that those talks went cold.