Kepa graduated from the University of the South Pacific with a Bachelor of Arts degree. She served as Principal of Corpus Christi College and then as a students' coordinator at the University of the South Pacific.
She succeeded her late sister, former Ro Lady Lala Mara, as Roko Tui Dreketi, or Paramount Chief of Dreketi, in 2004. This is considered to be the highest title in the Burebasaga Confederacy, one of three "confederacies", or tribal networks, of Fijian chiefs.
Ro Teimumu Kepa is the widow of Sailosi Kepa, a former High Commissioner to London, Minister of Justice and Attorney General (1988–1992), who went on to become a High Court Judge, Ombudsman, and first chairman of Fiji's Human Rights Commission.
In 1999 Kepa was appointed to the Senate. Following the 2000 Fijian coup d'état she was appointed as Minister for Women, Culture, and Social Welfare in the interim government of Laisenia Qarase. She contested the 2001 election as a candidate for the Soqosoqo Duavata ni Lewenivanua in the Rewa communal constituency, winning it with 2,636 votes. Following the election she was appointed as Minister for Education.
On 5 May 2005 she was elected as chairperson of the Rewa Provincial Council, a position previously held by her sister Ro Lady Lala Mara. This led to claims that she had forfeitted her seat in Parliament, resulting in her resigning from the council in August 2005.
In October 2005, Kepa was elected to the executive board of UNESCO, to which the Fijian government had nominated her in late September.
Kepa stood again for Rewa in the 2006 election, defeating her nephew, Ro Filipe Tuisawau. She was reappointed as Minister for Education, Youth and Sports in the multi-party cabinet. When the Qarase government was deposed by the 2006 Fijian coup d'état, Kepa joined a court case challenging the legality of the coup. She also used her position in the Great Council of Chiefs to oppose the coup, and was instrumental in the Council's 2007 rejection of Epeli Nailatikau nomination as Vice-President. As a result, the Council was suspended.
In May 2007, Kepa was threatened by the military over her opposition to the coup. However she continued to speak out against the regime and its People's Charter for Change, Peace and Progress. In July 2009 she was arrested and charged with breaching public emergency regulations and conspiracy to cause disorder after offering that her province would host the annual conference of the Methodist Church of Fiji and Rotuma, which the military regime had banned. The charges were later dropped. In 2011 the military regime suspended the Rewa Provincial Council in another effort to silence her.
In March 2014 Kepa was elected leader of the newly formed Social Democratic Liberal Party. She led the party into the 2014 election. The party won 15 of the 50 parliamentary seats; Kepa, who won 49,485 votes in her own name, was the second-highest ranked candidate behind Bainimarama.
On 6 October 2014 Kepa was appointed Leader of the Opposition.
In June 2016, Kepa announced that she was standing down as leader of SODELPA. She was replaced by former Prime Minister Sitiveni Rabuka.
In July 2016, Kepa was awarded a Peace Award by the Universal Peace Federation in Nepal and was accorded as a Global Peace Ambassador or Ambassador for Peace.