This paper proposes a wideband massive MIMO low Earth orbit (LEO) satellite system for integrated communications and localization (ICAL) in sixth generation (6G) networks. The system aims to simultaneously support wireless communications and localization operations in the downlink. The paper first characterizes the signal propagation properties and derives a localization performance bound. Based on these analyses, it focuses on the hybrid analog/digital precoding design to achieve high communication capability and localization precision. Numerical results demonstrate that the proposed ICAL scheme supports both wireless communication and localization operations for typical system setups. The paper discusses the potential of LEO satellite systems for ICAL due to their larger coverage, wideband communications, and flexible localization capabilities. It also explores the use of massive MIMO technology for ubiquitous ICAL, which provides numerous degrees of freedom in both temporal and spatial domains. The paper investigates the hybrid precoding design for the downlink of the ICAL systems, aiming to trade-off between the communication capability and the localization precision, measured by the spectral efficiency (SE) and the squared position error bound (SPEB). The paper proposes a hybrid analog/digital transmitter for wideband massive MIMO LEO satellite systems to perform ubiquitous ICAL by exploiting statistical channel state information (sCSI). The main contributions of the paper include the investigation of the upper bound of the ergodic SE expression, the derivation of a closed-form Cramér-Rao lower bound (CRLB) for the channel parameters, and the development of a hybrid precoding strategy and signal waveform design based on sCSI to simultaneously perform communications and localization. The paper also presents an algorithmic framework for designing the hybrid analog/digital precoders for the ICAL system to enable the trade-off between communication and localization performance. The paper concludes with simulation results and a summary of the proposed hybrid precoding approach for LEO satellite ICAL.This paper proposes a wideband massive MIMO low Earth orbit (LEO) satellite system for integrated communications and localization (ICAL) in sixth generation (6G) networks. The system aims to simultaneously support wireless communications and localization operations in the downlink. The paper first characterizes the signal propagation properties and derives a localization performance bound. Based on these analyses, it focuses on the hybrid analog/digital precoding design to achieve high communication capability and localization precision. Numerical results demonstrate that the proposed ICAL scheme supports both wireless communication and localization operations for typical system setups. The paper discusses the potential of LEO satellite systems for ICAL due to their larger coverage, wideband communications, and flexible localization capabilities. It also explores the use of massive MIMO technology for ubiquitous ICAL, which provides numerous degrees of freedom in both temporal and spatial domains. The paper investigates the hybrid precoding design for the downlink of the ICAL systems, aiming to trade-off between the communication capability and the localization precision, measured by the spectral efficiency (SE) and the squared position error bound (SPEB). The paper proposes a hybrid analog/digital transmitter for wideband massive MIMO LEO satellite systems to perform ubiquitous ICAL by exploiting statistical channel state information (sCSI). The main contributions of the paper include the investigation of the upper bound of the ergodic SE expression, the derivation of a closed-form Cramér-Rao lower bound (CRLB) for the channel parameters, and the development of a hybrid precoding strategy and signal waveform design based on sCSI to simultaneously perform communications and localization. The paper also presents an algorithmic framework for designing the hybrid analog/digital precoders for the ICAL system to enable the trade-off between communication and localization performance. The paper concludes with simulation results and a summary of the proposed hybrid precoding approach for LEO satellite ICAL.