Dr Mahathir Mohamad is now back with Umno after a two-hour meeting with new premier Najib Razak at his official residence in Putrajaya this morning.
He rejoined the party today together with his wife, Siti Hasmah and son, Mokhzani.
The former premier resigned in a huff last May 19 after a very public spat with his successor, Abdullah Ahmad Badawi.
KUALA LUMPUR: Malaysia's former premier Mahathir Mohamad on Saturday rejoined the ruling UMNO party which he quit last year and immediately pledged to strengthen the beleaguered party.
Mahathir left the party after falling out with his successor Abdullah Ahmad Badawi, who was replaced by Najib Razak on Friday as the new prime minister.
Mahathir, who spent more than two decades in power, had hand-picked Abdullah to replace him in 2003 but was enraged by Abdullah's decision to dismantle several of his pet projects.
"The image of UMNO has suffered in the last few years," Mahathir told reporters after handing over party membership forms to Najib, together with his wife Siti Hasmah and son Mokhzani Mahathir.
"The first thing is to clean the image of UMNO," he added.
Mahathir said he hoped his return would spur other former members to rejoin the party.
"I hope many other ex-UMNO members will return to the party. I am prepared to help UMNO regain the people's trust," he said.
UMNO, or the United Malays National Organisation, is the dominant political party in the country and leads the ruling Barisan Nasional coalition.
Mahathir last week endorsed a landmark speech by Najib in which he outlined radical reforms to UMNO following humiliating elections last year, when the opposition claimed five of the 13 states and a third of seats in parliament.
For a start, Mahathir said he would help campaign in two by-elections -- in Perak and Kedah -- to be held on Tuesday and which the opposition has expressed confidence in winning.
A third by-election will be held on the same day in the eastern Sarawak state of Batang Ai.
Mahathir defended his attack on the party leadership under Abdullah.
"I criticise UMNO because my criticism is to build UMNO ... not to destroy UMNO," he said.
Najib said Mahathir's return would help rejuvenate the party.
"Mahathir's return will revive the party and strengthen the Barisan Nasional," he said.
Najib takes office at a time when the economy is in dire straits and with minorities deserting the ruling coalition as demonstrated in the 2008 elections.