On 23 September 2015 a Memorandum of Understanding was signed between the IOI and the Australian and New Zealand Ombudsman Associaton (ANZOA).

The ANZOA is the peak body for Ombudsmen in Australia and New Zealand.

On 2 October 2018 a Memorandum of Understanding was signed between the IOI and the Association of Mediterranean Ombudsmen (AOM).

The AOM was founded in December 2008 during a second meeting of the network of Mediator and Ombudsman institutions in Marseille (France). The establishment of the Association is the result of the common engagement of the founding members, the Mediator of the Kingdom of Morocco, the Defender of People of Spain, and the Mediator of the French Republic. The AOM’s mission is the promotion and the defence of the fundamental rights in the countries of the Mediterranean basin. The common goal is to disseminate the principles of democracy and good governance. The members commit to make visible their engagements relating to the defence of these rights and thus contribute to the construction of a fair and equal society.

On 16 April 2013 a Memorandum of Understanding was signed between the IOI and the African Ombudsman and Mediators Association (AOMA).

AOMA encourages the establishment, development and promotion of African Ombudsman institutions and furthers mutual support, cooperation and joint activities through information sharing, training and development of Ombudsman and their staff.

On 20 October 2016 a Memorandum of Understanding was signed between the IOI and the Association of Ombudsman and Mediators of the Francophonie (AOMF).

Founded in 1998, the Association of Ombudsmen and Mediators of the Francophonie (AOMF) has 54 members across the continents in countries sharing French as a common language. The objectives pursued include promoting the Francophonie's knowledge of the role of the Ombudsman and the Ombudsman in serving citizens in order to strengthen their confidence in public services.

On 22 February 2018 a Memorandum of Understanding was signed between the IOI and the Association for the Prevention of Torture (APT).

The APT was founded in 1977 by the Swiss banker and lawyer Jean-Jacques Gautier. Over the past 40 years, the APT has developed a unique global overview and expertise in all aspects of the prevention of torture. It promotes transparency in all places where people are deprived of liberty and supports governments, justice systems and National Preventive Mechanisms (NPMs) to take effective actions to prevent torture and other ill-treatment.

In June 2017 a Memorandum of Understanding was signed between the IOI and the Caribbean Ombudsman Association (CAROA).

Established in 1998, CAROA is a member-based organization of Ombudsman offices in the Caribbean region. As of 2013, there are 15 Ombudsman offices established in the Caribbean region, of which 11 are functioning with Ombudsman in office.

On 15 May 2017 a Memorandum of Understanding was signed between the IOI and the Forum of Canadian Ombudsman (FCO).

The FCO was formed in 2000 by a group of ombudsman practitioners with a desire to provide a “home” for like minded individuals. FCO currently boasts more than 450 private and corporate members from all areas of Canada from the Atlantic to the Pacific to the Arctic coasts.

On 27 April 2016 a Memorandum of Understanding was signed between the IOI and the Federation of Ibero-American Ombudsman (FIO).

Created 20 years ago, FIO today brings together more than 75 Ombudsman institutions, from 20 Ibero-American countries and provides them with a forum for cooperation and the promotion, dissemination and strengthening of the Ombudsman concept.

In November 2020 a Memorandum of Understanding was signed between the IOI and the Global Alliance for Ministries and Infrastructures for Peace (GAMIP)

The Global Alliance for Ministries and Infrastructures for Peace (GAMIP) is a worldwide community of civil society campaigns, organizations, committed citizens, and government officials supporting the development of ministries and other infrastructures for peace.

On 13 November 2012 a Memorandum of Understanding was signed between the IOI and the International Anti-Corruption Academy (IACA).

IACA is an international organization located in Austria and founded in a joint initiative by the United Nations Office on Drugs and Crime (UNODC), the Republic of Austria, the European Anti-Fraud Office (OLAF) and other stakeholders. The organization functions as an independent centre of excellence in the field of anti-corruption education, training and academic research and offers training programs and a Master in Anti-Corruption Studies (MACS).

The 28th Annual Meeting of the International Coordinating Committee (ICC) of National Institutions for the Promotion and Protection of Human Rights in Geneva was marked by the official signing of a Memorandum of Understanding between the ICC and the IOI on 12 March 2015.

By signing this Memorandum of Understanding the leaders of both organizations emphasised the high value of this cooperation agreement and expressed their deep hope that members from both organisations will mutually benefit of this joint cooperation.

International Coordinating Committee (ICC) is now known as Global Alliance of National Human Rights Institutions (GANHRI).

On 27 October 2014 a Memorandum of Understanding was signed between the IOI and the Institute of Latin-American Ombudsman (ILO).

Created in 1984, ILO aims at encouraging the concept of ombudsmanship, contributing to the reinforcement of democratic processes and promoting and protecting human rights. Additionally to enhancing the concept of Ombudsmanship, ILO fosters related studies and seeks the creation of networks and cooperation amongst various Ombudsman institutions.

On 13 May 2016 a Memorandum of Understanding was signed between the IOI and the British and Irish Ombudsman Association (OA).

The OA is a professional association for ombudsmen and complaint handlers, their staff and others interested in the work of independent complaint resolutions.

On 19 September 2017 a Memorandum of Understanding was signed between the IOI and the OSCE Office for Democratic Institutions and Human Rights (ODIHR).

ODIHR is tasked with assisting OSCE (Organization for Security and Co-operation in Europe) participating States to ensure full respect for human rights, fundamental freedoms and the rule of law, to promote principles of democracy and to build, strengthen and protect democratic institutions. ODIHR also plays an important role in enhancing dialogue among states, governments and civil society.

On 12 May 2022 a Memorandum of Understanding was signed between the IOI and the United Nations Institute for Training and Research (UNITAR).

UNITAR supports governmental, non-governmental and international organizations in enhancing their capacities by offering customizable learning solutions that fit their respective needs.