Mr Anwar, 65, once belonged to the ruling Barisan Nasional (BN, National Front) coalition, but a falling out with top leaders resulted in him being beaten, jailed and disgraced.
Then came a political comeback, with him leading the opposition Pakatan Rakyat alliance into general elections in May 2013.
This three-party alliance posed the strongest-ever challenge to the coalition, which has governed Malaysia for more than half a century.
But it could not defeat BN - which won 133 of the 222 seats in parliament, its worst-ever election performance. The opposition won 89 seats, up from 82.
Quick ascent Mr Anwar first made his name as a student leader of a youth Islamic organisation, founding Malaysia's Islamic youth movement, ABIM.
His joining Malaysia's dominant party, United Malays National Organisation (UMNO), in 1982 came as a surprise to many but proved to be a good political move - he enjoyed a quick ascent up the political ladder and held multiple ministerial posts.
In 1993 he became Prime Minister Mahathir Mohamad's deputy and was widely expected to succeed him, but tensions grew between the two men, particularly over issues like graft and the economy.
In September 1998, Mr Anwar found himself sacked and eventually charged with sodomy and corruption.
The trial which followed led to a six-year jail term for corruption and also sparked huge street protests.
In 2000 he was then found guilty of sodomy with his wife's driver and jailed for a further nine years, to be served concurrently with his other sentence.
While homosexual acts are illegal in Muslim-majority Malaysia, very few people are ever prosecuted. Mr Anwar has always maintained the charges were part of a political smear campaign.
In late 2004 Malaysia's Supreme Court overturned the sodomy conviction, freeing him from jail.
'Shared policy' Upon his release, he emerged as the de facto head of a newly-invigorated opposition that registered a strong showing in the 2008 elections.
The opposition gained more than a third of parliamentary seats and control of five states, partly due to public discontent over corruption and discrimination issues.
A High Court eventually cleared Mr Anwar of the charges in January 2012, citing a lack of evidence.
In the 2013 general election, Mr Anwar led the opposition into what was seen as the country's most hotly-contested polls to date.
The three-party opposition comprised Mr Anwar's multi-racial party, a secular Chinese-majority party and a conservative party of Muslim Malays.
The Pakatan Rakyat promised bold changes, including doing away with race-based policies that it says breed corruption and hamper economic growth. It instead pushed for a more competitive system based on merit.
The alliance also said it was seeking to end monopolies in certain sectors and free up civil liberties.
This played well with young voters, in cities and with Chinese voters - but in the end was not enough to unseat the ruling coalition, who Mr Anwar accused of electoral fraud.
Ahead of the polls, Mr Anwar said he would step down as opposition leader if his alliance was defeated.
"People have to accept that I have given all that I have," he said. "I have given a lot of my personal life and suffered immensely."

bbc.com