Ranko founded and led the Business Finance (BF) research group from 2016 to 2026. His research interests include: corporate and entrepreneurial finance, private equity, sustainable finance, and bond markets. He has published over forty academic journal papers and book chapters and has been ranked among top 10% authors on the Social Sciences Research Network (SSRN) by number of citations and paper downloads. His papers featured on the SSRN’s Top Ten lists in areas of Economics, Econometrics, Law and Finance, Corporate Governance, etc. He is ranked among Top 3% authors in Economics and in All Fields by ScholarGPS. His Google Scholar i10 and h-index are 28 and 21, respectively. Ranko’s publications were selected as showcase publications by academic journals and received the highest quality rating. Ranko's work has been commented on and referenced in the Financial Times and other media outlets. He received research grants from the Economic and Social Research Council (ESRC), Institute for Quantitative Investment Research (INQUIRE), Association of Certified Chartered Accountants (ACCA), and African Development Bank (ADB). He was also a recipient of the World Bank (IBRD) and Institute of Chartered Accountants of England and Wales (ICAEW) scholarships for his postgraduate studies. 

Ranko has teaching experience at several UK (LSE, Hull, Birmingham) and overseas (EDHEC-Lille & Nice, Belgrade) universities. He was also teaching on executive MBA and DBA programmes in UK, Singapore, Hong Kong, Malaysia, and Mauritius. Ten of his PhD students took up academic positions at UK and overseas universities. He received University of Birmingham award for excellence in doctoral supervision. He held various academic positions (e.g. School Director of Research, Head of Department, Convenor of PhD programmes, etc.) and served as external examiner on programmes delivered by universities (Imperial, Manchester, LSE, Cranfield) and professional bodies (ACCA). Ranko was elected board member of European Financial Management Association and has served as an associated editor of the European Journal of Finance since 2017.