At present, in the Bangkok Metropolitan Area of Thailand, numerous construction projects are in process or have recently been brought to completion. In pursuing this work, contractors regularly face construction delay problems, many of which are likely to have been avoidable. The research objective is to survey and prioritize the factors leading to construction delays from the perspective of both the consultants and the contractors. Data were collected via a survey instrument and the Delphi technique was used as the research methodology. To identify the factors that lead to construction delays relevant to the study context, a panel of experts comprising 18 construction public company leaders and 17 project engineers and 17 project consultants, 1 from each of the largest construction contractor and consultant companies in Thailand, and 20 academics in the field of construction were invited to share their opinions. Eventually, 13 factors leading to construction delays were identified from the data collected from the expert panel. A questionnaire was generated using a Likert scale with a range of 1–5 based on the factors suggested by the experts’ opinions. A total of 17 respondents from the contractor companies and 17 respondents from the consultant companies responded to the questionnaire. The numeric value of the responses was computed using the Delphi technique. The responses reached constancy at the second round of data collection. According to the statistical analysis, a Shortage of qualified labor was the most important factor leading to construction delays, according to both the contractors’ and the consultants’ perspectives with a mean value of 4.65 and 4.53, respectively. Change orders made by owners were the second most important factor according to both the contractors and the consultants with a mean value of 4.24 and 4.28, respectively. In addition, insufficient financial liquidity on the part of the contractor ranked as the third most important reason according to both the contractors and the consultants with a mean value of 4.18 and 4.12, respectively. The outcomes are applicable to the causes of construction delay in the Bangkok Metropolitan Area of Thailand, but may not be applicable to other settings. A review of the literature suggests significant differences in relation to such matters as the regulatory environment, societal practices and expectations, economic considerations, the environment, technology, and religion across settings may have an impact on what causes construction delays.