This study investigates the relationship between human resource planning and organisational sustainability in selected telecommunication firms in Port Harcourt, Nigeria. Adopting a cross-sectional survey design, data were collected from five randomly selected telecom firms. A total of 95 questionnaires were distributed to supervisors, HR managers, and general managers, with 82 valid responses returned. The study measured key dimensions of human resource planning—including required personnel, competence, age, and culture—using a 5-point Likert scale. Data analysis was conducted using Spearman’s Rank Correlation Coefficient via SPSS version 22.0. Findings reveal a significant positive relationship between human resource planning and organisational sustainability. Specifically, factors such as employee competence, cultural fit, and age diversity were found to enhance long-term organisational viability. The study concludes that strategic HR planning plays a vital role in sustaining organisational performance. It recommends that HR professionals prioritize applicant competence and cultural alignment during the recruitment process to foster sustainability.