Thulani Maseko was shot dead on Saturday night by unknown attackers in Luhleko, about 50km (30 miles) from the capital Mbabane, opposition spokesman Sikelela Dlamini said.
The United Nations human rights chief has called on Eswatini to swiftly and impartially investigate the brutal killing of prominent opposition politician and human rights lawyer Thulani Maseko.
"Thulani Maseko was a stalwart of human rights who, at great risk to himself, spoke up for many who couldn't speak up for themselves," Volker Turk said in a statement on Monday.
"His cold-blooded killing has deprived Eswatini, southern Africa and the world of a true champion and advocate for peace, democracy and human rights."
Maseko was shot through the window while he was inside with his family, the spokesman said.
In his statement, Turk called on the Eswatini authorities "to ensure a prompt, independent, impartial and effective investigation is held into his killing... and to hold all those responsible to account in fair trials".
Maseko, a leading human rights lawyer and columnist, was the founder of the Multi-Stakeholder Forum (MSF) - a coalition of opposition parties, associations and churches.
I’m horrified by Thulani Maseko’s @thulanirudolfm1 bloody murder in his home! Shame on you, @KingMswatiIII for the cowardly act of hiring hitmen to murder those who challenge your authoritarianism by calling for democracy in Eswatini! I join the world to demand #Justice4Thulani! pic.twitter.com/JhHOltuRXD— Stella Nyanzi (@drstellanyanzi) January 23, 2023
In 2014, he was jailed for contempt of court over articles critical of the government and judiciary, but was acquitted on appeal and released a year later.
And he had a pending court battle with King Mswati III over the monarch's decision to rename the country Eswatini by decree.
The country's name was changed from Swaziland to Eswatini to mark the 50th anniversary of its independence from Britain in 2018.
Maseko's position was that the king had not followed the constitution in the process.
And at the time of his death, he was the legal re presentative for two members of parliament facing trial for offences allegedly committed during the civil unrest that rocked Eswatini in 2021, according to the UN rights office.
Maseko's death came just hours after the king challenged activists fighting to end Africa's last absolute monarchy.
"People should not shed tears and complain about mercenaries killing them," King Mswati had said.
In addition to calling for an investigation of Maseko's death, Turk demanded on Monday that the Eswatini authorities "ensure the safety and security of all Eswatini people, including human rights defenders, journalists and political activists and protect civic space".