HIW was formed in 1930/1931 as a merger between the minor National and People's parties and other like-minded nationalist groups.[8] It gathered opponents of then Prime Minister Nuri Pasha al-Said who had concluded the Anglo-Iraqi Treaty of 1930.[2] The new party soon gained the support of Jam'iyat Ashab al-San'a (Artisans' Society), the largest trade union in Iraq.[9] The party held its first meeting in Baghdad in March of the same year, attracting 2000 followers to a rally where they called for a new government and a redefinition of the relationship between Iraq and the United Kingdom.[10] In order to demonstrate its importance the party organised strikes in July, although there was no direct political motive behind the move, other than showing that the HIW had support.[11]
The party formed a pact with the Nationalist Party in 1932 and used this to gain influence in the Iraqi parliament.[12] With this influence secured they forced out the government of Naji Shawkat and soon established an HIW government, despite the fact that the majority of the chamber had been elected on an anti-HIW ticket.[13] However the initial government was not to last long as advisers close to the new king Ghazi convinced him that the HIW government was responsible for tribal unrest. As such the government was removed and al-Kaylani and his right-hand man Yasin Pasha were to be excluded from future governments.[14] This remained the case for future HIW administrations, although al-Kaylani returned to the top job after Ghazi's death.
During the Kingdom of Iraq period that party supplied the Prime Minister on five occasions. Those governments identified as Party of National Brotherhood were:
Rashid Ali al-Gaylani, March 20, 1933 – November 9, 1933
Yasin al-Hashimi, March 17, 1935 – October 30, 1936 (partnership with the military)
