While the burden of caring for older people with chronic medical illness and dementia has been well documented, considerably less is known about how carers develop the strength and resilience to sustain this important role with older family members with mental illness. The aim of the study was to understand the lived experience of primary caregivers of older people with severe and persistent mental illness, and to explore what, if anything, helps to sustain them in their caring role. An interpretative phenomenological analysis approach was adopted, and qualitative interviews were used with 30 primary caregivers. Two overarching themes, and related subthemes, were abstracted from the data. First, caring is a difficult and demanding responsibility. It affects carers adversely, emotionally, physically, socially, and financially, and their lifestyle in general. This is reflected in three subthemes: (i) physically and emotionally draining; (ii) grieving about the loss; (iii) and adverse effects on lifestyle and social relationships. Second, carers develop resilience in caring, which helps sustain them in their role, as illustrated in three subthemes: (i) caring as purposeful and satisfying; (ii) harnessing social support from others; and (iii) purposefully maintaining their own well-being. Community mental health nurses have a key role in assessing carers’ needs and supporting them in their caring role.