Lyall Bay is a bay and suburb located on the south side of the Rongotai isthmus in Wellington, New Zealand. It serves as a residential area within the city, bordered by Te Raekaihau Point to the southwest which divides it from Houghton Bay. The suburb encompasses most of the southern half of the isthmus, though the airport and adjacent industrial zones are often considered part of Rongotai.

The bay was likely the ancient mouth of the Hutt River before geologic upheaval created the current isthmus through earthquakes like the 1855 Wairarapa event. Originally named Maranui by H D Crawford and H M Hayward in 1896, the suburb developed rapidly after a tram line extension reached the beach in December 1909. Early development faced challenges from sand drift, leading to council interventions including dune leveling and sea walls.

The area is defined by its surf beach, which features a breakwater at the eastern end known as Surfers Corner. The beach has shrunk to two-thirds of its original size due to airport construction. Key landmarks include the Southern Headlands Reserve, Wellington International Airport, and the distinctive whirler sea wall built in 1932. The suburb also contains the Southern Walkway and a small industrial area.

Lyall Bay is a popular destination for surfing and swimming, having hosted surf lifesaving championships. Duke Paoa Kahanamoku helped popularize surfing here in 1915. The beach is home to two surf lifesaving clubs, Lyall Bay and Maranui, which patrol the waters. The area attracts visitors for its safe swimming conditions and vibrant surf culture, supported by local amenities like a Playcentre and lawn bowls club.

The statistical area covers 0.55 km2 with an estimated population of 2,680 as of June 2025. The median age is 36.6 years, and the median income is $56,100. Transport access includes a bus service and proximity to the Kilbirnie shopping centre. The suburb features a primary school, churches, and shops, with a diverse population reflecting 75.3% European and 13.4% Māori identification in the 2023 census.