[8][10] Malloch Brown contemplated running for the Social Democratic Party at the 1983 United Kingdom general election but was not selected as a candidate.
[8][14][15] In Colombia, he advised the government on how to shed "its image as the political wing of the Medellin cartel"[14] In the Philippines, Malloch Brown worked with Corazon Aquino in the campaign against Ferdinand Marcos.
[17] In 1994, Malloch Brown joined the World Bank as Vice-President for External Affairs, which included responsibility for relations with the United Nations.
[19] In late 2002, Malloch Brown offered to assist talks between Hugo Chavez's Bolivarian government and the opposition, who was seeking to begin the process of attempting to recall Chávez a year later.
[6] In January 2005 he was appointed Chef de Cabinet to UN Secretary-General Kofi Annan, whilst retaining his position as Administrator of UNDP for much of 2005.
[8][23] Malloch Brown succeeded Louise Fréchette as United Nations Deputy Secretary-General on 1 April 2006, retaining the position until December 2006.
[6] In 2006, he was named a visiting fellow at the Yale Center for the Study of Globalization and announced plans to focus on writing a book on changing leadership in a globalised world while in residence during the spring semester.
[25] Malloch Brown, briefing the Security Council, argued that, while the situation uncovered by the audit was "alarming", and that nearly $300 million out of a $1.6 billion budget was involved, it showed more that there was significant waste with only narrow instances of fraud.
He stated that much of the political dialogue in the US about the UN had been abdicated to its most strident critics, such as conservative talk-show host Rush Limbaugh and the Fox News cable channel and, as a result of this, the true role and value of the UN has become "a mystery in Middle America".
[28] These remarks resulted in a backlash from the White House and some US conservative commentators, culminating in a call for an apology by the US envoy to the United Nations John Bolton.
... Mr. Malloch Brown is surely correct: the people of the United States deserve better leadership and diplomacy to represent their interests in the world’s most important international body.
"[30] Malloch Brown himself rejected the need to apologise and received the support of Secretary-General Kofi Annan, who said that his deputy's comments "should be read in the right spirit".
[38] At the time, The Daily Telegraph said "While the aid agencies and liberals were still toasting the arrival of 'Saint Mark' to Whitehall, the neo-cons on both sides of the Atlantic were throwing darts at photographs of their devil.
[He] divides opinion between those who see him as the great hope for Africa and a principled opponent of the war in Iraq, and those who believe that he is an anti-American egotist who defended Kofi Annan over the oil-for-food scandal.
[42] In November 2007, the conservative British magazine The Spectator drew some attention with its criticism of the Malloch Brown family's occupancy of a government-owned, so-called "grace and favour" apartment in London, previously used by former Deputy Prime Minister John Prescott.
[51][52] Among his non-governmental and private sector roles, Malloch Brown became chairman of the board of directors of SGO Corporation Limited, a holding company whose primary asset is the election technology and voting machine manufacturer Smartmatic, in 2014.