Worthing is situated on the West Sussex coast in South East England, 49 miles (79 km) south of London and 10 miles (16 km) west of Brighton and Hove. It forms part of the Brighton/Worthing/Littlehampton conurbation along with neighbouring towns and villages in the county such as Littlehampton, Findon, Sompting, Lancing, Shoreham-by-Sea and Southwick. The area is the United Kingdom’s twelfth largest conurbation, with a population of over 460,000. The borough of Worthing is bordered by the West Sussex local authority districts of Arun in the north and west, and Adur in the east. The town is dominated by the Downs to the north: Cissbury Ring, a Site of Special Scientific Interest, rises to 184 metres (604 ft) in the north of the borough. A further high point is at West Hill (139m) north-west of High Salvington

Lying on the south coast of England, Worthing is situated on a mix of two beds of sedimentary rock. The large part of the town, including the town centre is built upon chalk (part of the Southern England Chalk Formation), with a bed of London clay found in a band heading west from Lancing through Broadwater and Durrington. There are no major rivers within the borough, however the culverted Teville Stream begins as a spring in what is now allotments in Tarring, runs along Tarring Road and Teville Road north of the town centre, passing to the east through Homefield Park and Davison High School before meeting the sea at Brooklands where the Broadwater Brook meets the sea. To the west and also in parts culverted, Ferring Rife rises in Durrington near Littlehampton Road, passing through Maybridge, then west of Ferring into the sea.

Being located in the South Coast Plain at the foot of the South Downs, some of the undeveloped land in the north of the borough is proposed to form part of the South Downs National Park. The west of the borough contains some ancient woodland at Titnore Wood. The development along the coastal strip is interrupted by strategic gaps at the borough boundaries in the east and west, each gap falling largely outside the borough boundaries. The southwest of the borough contains part of the Goring Gap, a protected area of fields and woodland between Goring and Ferring. To the east of Worthing lies the Sompting Gap, a protected area that lies between Worthing and Sompting. This area was formerly an inlet of the sea and it is here that the Broadwater Brook (also known as Sompting Brook) flows into Brooklands Park and on into the sea. Some of the reedbeds in the Sompting Gap at Lower Cokeham have been designated a Site of Nature Conservation Importance. The borough of Worthing contains no nature reserves: the nearest is Widewater Lagoon in Lancing.