Jailed Rwandan gospel singer, Kizito Mihigo's, request for a separate appeal hearing was on Monday denied by the Supreme Court.
The judges ruled that Mr Mihigo must appear alongside his accomplice.
The 37-year-old was in February 2015 sentenced to a reduced sentence of 10 years after admitting to a plot to kill President Paul Kagame.
He was convicted alongside radio journalist Cassien Ntamuhanga, who was handed 25 years, and retired soldier Jean Paul Dukuzumuremyi, who got 30 years.
The three appealed their sentences.
However, Mr Ntamuhanga is now a fugitive after escaping from prison in October last year.