DÍAZ-HEREDERO Legal & Tax

Professional profile

Portrait of Gonzalo Díaz-Heredero López

Gonzalo Díaz-Heredero López

Gonzalo Díaz-Heredero López is a jurist, a graduate in Law and in Business Administration from the Complutense University of Madrid (bilingual programme). His work concentrates on tax, tax procedures and civil law.

His background combines three distinct environments: a tax boutique, where he advised a portfolio of Spanish and international companies as well as resident and non-resident individuals; a civil litigation firm, where he worked on complex matters at first instance and on appeal; and the tax litigation department of an energy sector multinational, where he prepares opinions and reports on one of the most technical areas of Spanish tax law.

Alongside that practice runs his own line of work on artificial intelligence applied to law, recognised with two awards and with academic and professional publications.

Currently completing the qualifying programme for admission to the Spanish Bar. He does not practise as an admitted lawyer and does not provide court representation or advocacy.

  • Spanish

    Native

  • English

    C2 Proficiency

  • French

    B2

Professional experience

  1. Repsol S.A.

    Legal Trainee · Tax litigation

    March 2026 – present

    • Preparation of highly complex legal opinions and reports in the energy sector (regional band of the hydrocarbon tax, hydroelectric levy, electricity production tax, excise duties).
    • Support in preparing administrative review appeals (reconsideration, hierarchical appeal and economic-administrative claims) and judicial review proceedings, including matters with potential access to cassation before the Supreme Court.
    • Support in designing the procedural strategy.
    • Review of administrative files: agreed and contested audit reports, assessment decisions and penalty decisions relating to excise duties, corporate income tax, VAT and local taxes.
    • Preparation of statistical reports and monitoring of tax developments.

  2. Bufete Arroyo Romero

    Legal Trainee · Civil litigation

    September 2025 – February 2026

    • Preparation of legal opinions, statements of claim, defences, interlocutory submissions and appeals, as well as responses to appeals.
    • Support in complex civil disputes at first instance and on appeal: enforcement proceedings, auctions and collection proceedings, monetary claims and contractual disputes.
    • Family law, property rights and succession matters, including judicial division of estates.
    • Preparation of administrative tax appeals concerning local taxes.
    • Applied research on legal technology.

  3. Bové Montero y Asociados

    Intern and Junior · Tax and Legal Department

    May 2024 – September 2025

    • Ongoing tax advice to a portfolio of Spanish and international companies: permanent establishments, foreign securities holding companies, M&A transactions, real estate taxation, corporate income tax and VAT.
    • Management of a portfolio of resident and non-resident individuals: personal income tax, wealth tax, international taxation and reporting obligations.
    • Drafting of administrative appeals and submissions; support in management, audit and collection proceedings.
    • Support in tax due diligence and tax compliance processes.
    • Tax filings and tax accounting.

Recognition

15th ISDE International Legal Award 2025 — student category

Instituto Superior de Derecho y Economía (ISDE)

Awarded for the dissertation “Analysis of the exemption under Article 7 p) of the Personal Income Tax Act for employment income earned abroad”, on one of the most disputed exemptions in Spanish personal income tax, of particular relevance to international taxation and worker mobility.

13th UCM University Entrepreneurship Awards 2025 — dissertation category

Complutense University of Madrid · Score 96.5/100

Distinction awarded to the dissertation “Identification of Unconventional Patterns in Double Taxation Agreements” for its innovation and its contribution to fostering entrepreneurship. The work applies natural language processing models to the comparative analysis of double taxation agreements.

Education

  1. ISDE

    LLM in International Advocacy

    June 2026 – January 2027

  2. Universidad Internacional de La Rioja (UNIR)

    Máster de Acceso a la Abogacía y la Procura (qualifying master’s degree for admission to the Spanish Bar)

    September 2025 – January 2027

    • In progress. Qualifying programme for admission to the Spanish Bar.

  3. Complutense University of Madrid

    Double Degree in Law and Business Administration (bilingual programme)

    2019 – 2025

    • Business Administration dissertation awarded with honours (Top 1%): “Identification of Unconventional Patterns in Double Taxation Agreements: An Analysis Based on AI-Assisted Natural Language Processing Models”.
    • Law dissertation: “Analysis of the exemption under Article 7 p) of the Personal Income Tax Act for employment income earned abroad”.
    • Member of the debating society.
    • French courses B2.1 and B2.2 at the UCM Centre for Modern Languages.

  4. Warsaw School of Economics

    BBA · Erasmus programme

    September 2022 – February 2023

Further training

Fundación Mutualidad

Legal Entrepreneurship Lab (2026)

Entrepreneurship training programme for the legal sector.

Banco Santander

Santander X Explorer

Twelve-week entrepreneurship programme; development of a legal technology project.

Tools and technical skills

  • Python applied to the analysis of legal and tax data.
  • Legal technology and generative AI tools in a professional environment.
  • Case law and doctrinal research in Aranzadi, CENDOJ and specialist legal databases.
  • Statistical analysis of tax litigation and of revenue indicators.
  • Workflow optimisation and automation.

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