In healthcare, moving and handling people (MHP) often cause musculoskeletal disorders. To prevent musculoskeletal disorders due to MHP, many national evidence-based guidelines have been developed. However, little is known about how these guidelines were intended to work, i.e. their \'programme theory\', how implementation by intended users is influenced by contextual factors and mechanisms to produce outcomes. This paper identifies the programme theory of a national MHP guideline (MHPG) using thematic analysis of the MHPG document, three organisational planning documents, and interviews with MHPG developers. The analysis identified the intended users of the MHPG as health and safety managers and MHP coordinators. The programme theory comprised contextual factors, potentially hindering (e.g. budget constraints) or facilitating (e.g. changing demographics) implementation, being influenced by mechanisms mainly based on ethical (quality of care, evidence-based practices), and economic reasoning (reducing cost of MHP, return on investment) to reduce injuries caused by MHP - the intended outcome.