This study aims to examine the collaborative efforts of public and school libraries to implement lifelong learning targets. Using data collected from school and public library staff, head teachers and education officers in Zanzibar, this study seeks to obtain opinions regarding public library support provided to school libraries, types of collaborative programs that public and school libraries engaged in to attain lifelong learning targets, and the effectiveness of library joint programs in promoting lifelong learning opportunities. The study used a cross-sectional design, whereas a mixed approach through the convergence method was used to collect, analyze and interpret data. A non-probability sampling under purposive sampling techniques was applied to select respondents for this study. Primary data was collected through a survey method using a structured standardized questionnaire, face-to-face interviews and focus group discussions. A total of 36 public library staff and 94 school library staff filled out questionnaires. Interviews were conducted with 42 respondents while 18 respondents were involved in focus group discussions. Findings revealed the existence of collaborative efforts between public libraries and school libraries. However, there were neither collaborative plans nor assessment and evaluation strategies, thus, the program's implementation did not guarantee the effective promotion of lifelong learning opportunities for all. The study recommends that the education authorities should address and prioritize the agenda of lifelong learning by introducing a national-wide library collaboration campaign toward the implementation of SDG 4 targets along with the improvement of public and school libraries' capacity in terms of staff and resources. [ABSTRACT FROM AUTHOR]