Marco Di Siena was an officer in effective permanent service of the Italian Financial Police (Guardia di Finanza) from 1989 to 2002. He has held numerous positions in the operational and staff until 2002 when he took his leave. He has immediately started collaborating with Chiomenti of which he became a partner in 2011. he is part of the Tax Law Department of the Firm.

He is the author of numerous publications on business income and performs an intense doctrinal activity in the main scientific journals in the sector. He has he published three monographs on tax matters and is a member of the committee editor of the Quarterly Review of Tax Law and of the Law Review Tax on-line. He was adjunct professor of tax law at more Italian universities as well as lecturer at the School of Economic Administration  and School of Financial Police. He usually carries out conference activities and holds interventions at the university and as part of post-training initiatives in the fiscal field.

In his professional activity he assists Italian and foreign clients mainly in the field of business income and patronizes in tax litigation matters.