The party was initially founded as United People's Party in 2014 at Sarawak with its headquarters based at Kuching. The UPP was started as a pro-Barisan Nasional political party and a splinter party of Sarawak United People's Party set-up by the Second Finance Minister for Sarawak, Wong Soon Koh and his supporters following a leadership tussle of the party then. However the hopes that the UPP would join BN were objected by the coalition leadership. UPP rejected Parti Pesaka Bumiputera Bersatu secretary general Dr Stephen Rundi Utom's suggestion that UPP should dissolve to pave the way for its members to join other BN component parties arguing that they have over 26 full-fledged branches with 30,000 members and that UPP was able to raise RM38 million for an education fund in less than a fortnight. UPP's ability to raise significant funds is widely attributed to the support they enjoy from Sarawak's powerful timber tycoons. A Memorandum of Understanding was made between UPP and SUPP of BN for the division of seats to be contested in the 2016 Sarawak state election which saw UPP win five out of seven seats it was allocated. UPP however cancelled the MoU with SUPP after the 2016 state election. Both parties again signed MoU for collaboration in the 2018 general election. After the GE14 which saw the downfall of BN federal government, the state government coalition components quit BN and formed themselves as the new Gabungan Parti Sarawak coalition without UPP.
Re-branding as Parti Sarawak Bersatu (PSB)
UPP was re-branded to Parti Sarawak Bersatu, after delegates of its extraordinary delegates conference on 8 December 2018 unanimously voted to amend the party's constitution and the Registrar of Societies had approved the name change as well as the party's new logo in 2019. PSB amid being left out of newly formed GPS coalition, choose to maintain its status quo, but shift from BN to GPS friendly party by providing supply and confidence to the new GPS coalition Sarawak state government. Somehow the party status changed when PSB opted to be an independent instead with its president, Wong tendered his resignation from the state Cabinet as the International Trade and e-Commerce Minister and second Minister of Finance in July 2019.
During the 2020 Malaysian political crisis, the support inclination of PSB Sri Aman MP; Masir Kujat, for the tussling parties, has been in much speculation of the political scene. Despite being arranged to be seated alongside the new governing Perikatan Nasional backbencher MPs in the Dewan Rakyat during the historic the one-day Parliament sitting on 17 May, Masir has clarified that he and the PSB party is still in the opposition bloc in the federal and state levels. Impact of the political crisis had also witnessed 2 former top Sarawak People's Justice Party figures; Selangau MP cum Ba Kelalan assemblyman Baru Bian and Batu Lintang assemblyman See Chee How, together with their supporters have joined PSB on 30 May 2020.
