It is a burrow-nesting annual breeder, laying in mid-October to mid-November (ACAP 2009). Chicks usually fledge in late April (Barbraud et al. 2009). Outside the chick-rearing period, White-chinned Petrels breeding on South Georgia travel to the Patagonian shelf to feed. White-chinned Petrels breeding on the Falkland Island (Islas Malvinas) also largely winter in the Patagonian shelf, but some migrate to waters off southern Chile (Phillips et al. 2006, Rexer-Huber et al. in litt. 2016). Satellite tracking and ring recoveries from birds on Crozet Islands show that they spend the non-breeding season off the coasts of South Africa and Namibia (Barbraud in litt. 2008), while non-breeding birds from Marion Island winter mainly off South Africa (GLS; Rexer-Huber et al. in litt. 2016). Individuals from the Kerguelen Islands also winter off the coasts of South Africa and Namibia over the Benguela Current (Péron et al. 2010b). Non-breeding White-chinned Petrels from the Auckland Islands winter off the coast of Peru, Ecuador and northern Chile (Rexer-Huber et al. in litt. 2016), while those from the Antipodes winter off Peru and Chile (Sommer et al. 2010).
The species feeds on cephalopods, crustaceans and fish (Berrow and Croxall 1999, Catard et al. 2000, Delord et al. 2010) and processing waste from fisheries or discarded longline baits. Birds range widely when searching for food resources, travelling up to 8,000 km on feeding forays in the breeding season (Berrow et al. 2000b, Catard et al. 2000, Phillips et al. 2006, Delord et al. 2010). Individuals breeding at the Crozet and Kerguelen Islands display a bimodal foraging strategy, conducting either short trips to the surrounding shelf or long trips ranging from subtropical waters in the north to Antarctic waters in the south (Catard et al. 2000). Individuals breeding at the Kerguelen Islands target the seasonal ice zone where melting sea ice is gradually broken into floes and forage almost exclusively in open water (Péron et al. 2010b). 

The main threat faced by this species is high rate of incidental mortality in longline fisheries, although bycatch mitigation measures are returning a significant decrease in mortality. Barbraud et al. (2009) estimated that any additional source of mortality that approaches 31,000 individuals would result in a population decline at the Kerguelen Islands. Only 30% of this number are killed in local waters, and even fewer are now killed due to the implementation of mitigation measures. However, many birds are killed in the waters of Namibia and South Africa, which make up the majority of the Benguela Current Large Marine Ecosystem, where individuals from the Kerguelen Islands spend the winter. As such, this has the potential to cause declines in the Kerguelen Islands population. The Namibian hake longline fishery is historically thought to represent one of the largest legal sources of bycatch, with an estimated 20,567 birds killed in 2010, of which White-chinned Petrels represented 85% (BirdLife International 2017). However, the Namibian government has taken steps to introduce fishery regulations enforcing boats to take measures to mitigate bycatch. This uses bird-scaring lines (BirdLife International 2014, 2015), which have been shown to reduce White-chinned Petrel bycatch by over 90% (Paterson et al. 2017), and better line-weighting to reduce the time taken to sink the baited hooks out of range of seabirds (BirdLife International 2014, 2015). In the South African hake trawl fishery, prior to the use of bird-scaring lines, approximately 1,800 individuals were killed annually (Watkins et al. 2007), with the species attending 99% of trawls (Hill 2006). However, in 2006, bird-scaring lines became a requirement to gain a vessel permit, likely resulting in reduced bycatch. Discards from the South African deep‐water hake fishery make up more than half the diet of white‐chinned petrels (Jackson 1988, Crawford et al. 1991 per Watkins et al. 2007), likely increasing their vulnerability. It is estimated that the combined bycatch of South African pelagic and demersal fisheries amounts to 186 White-chinned Petrels annually (Petersen et al. 2007).

It is thought that fishery-related mortality exerts a greater pressure on the Indian Ocean population than the Atlantic Ocean population (Ryan et al. 2012). In the Indian Ocean, between 2001 and 2003 the legal longline fishery for Patagonian Toothfish Dissostichus eleginoides killed around 12,400 White-chinned Petrels per year (Delord et al. 2005). Following the introduction of mitigation measures, this figure dropped to approximately 2,500 birds in the 2005-2006 season (CCAMLR 2006), and to 740 birds in the 2008-2009 season (CCAMLR 2010). In addition to this, a further 31,000-111,000 and 50,000-89,000 seabirds were killed by illegal, unreported and unregulated fishing vessels in 1997 and 1998 respectively, around 60% of which were White-chinned Petrel (CCAMLR 1997, 1998). However, by 2006, this figure had fallen to 4,583 seabirds killed (CCAMLR 2006). The White-chinned Petrel is one of the species most commonly found attending longline vessels off south-east Brazil during winter (Olmos 1997, Bugoni et al. 2008) and off Uruguay (Jiménez et al. 2009). Artisanal fisheries off the South American coast have been demonstrated to cause significant bycatch mortality and very large numbers of small longlining vessels are the primary concern (Mangel 2012). It is the second most commonly-caught species in the Argentinean longline fleet, with an average capture rate for the period 1999-2003 of 0.014 ± 0.09 individuals per 1,000 hooks (Laich and Favero 2007). In the Australian Fishing Zone, more than 800 individuals are potentially killed annually (Gales et al. 1998) and in New Zealand between 2003 and 2005, 14.5% of all the seabirds caught in trawl and longline fisheries and returned for autopsy were P. aequinoctialis (Baird and Smith 2007).

Historically, human exploitation is thought to have caused extinction on the Chatham Islands (Carboneras et al. 2014). More recently, White-chinned Petrels have been targeted by an illegal artisanal fishery in Southern Angola for their meat and the use of their livers as bait (Petersen et al. 2007), however, this is not known to have caused a significant population decline.