The objective was to identify factors associated with decisions made by patients with amyotrophic lateral sclerosis (ALS) to accept or decline non-invasive ventilation (NIV) and/or gastrostomy in a prospective population-based study. Twenty-one people with ALS, recruited from the South-East ALS Register who made an intervention decision during the study timeframe underwent a face-to-face in-depth interview, with or without their informal caregiver present. Sixteen had accepted an intervention (11 accepted gastrostomy, four accepted NIV and one accepted both interventions). Five patients had declined gastrostomy. Thematic analysis revealed three main themes: (1) patient-centric factors (including perceptions of control, acceptance and need, and aspects of fear); (2) external factors (including roles played by healthcare professionals, family, and information provision); and (3) the concept of time (including living in the moment and the notion of 'right thing, right time'). Many aspects of these factors were inter-related. Decision-making processes for the patients were found to be complex and multifaceted and reinforce arguments for individualised (rather than 'algorithm-based') approaches to facilitating decision-making by people with ALS who require palliative interventions.