Mr Johnson died in the early hours of Friday after a brief illness in Port Harcourt, Rivers State capital.
In a statement by the president’s spokesman, Garba Shehu, Mr Buhari said he received the news with deep sadness.
The statement read, “The President joined PENGASSAN and all Labour Unions in the country in mourning the visionary leader, whose good nature, understanding and forthrightness helped in improving the welfare of workers, and contributed immensely to the stability witnessed in the oil sector.”
Buhari affirmed that “Johnson’s broadmindedness and generosity of spirit by always putting the nation first before all pecuniary gains shaped ease of relationship and smooth operations in the oil sector between employers and workers, recognising his wise and considerate positions in all negotiations.”
The President also said Johnson’s demise “is a collective loss to the family, labour movement and the entire nation.”
He urged all loved ones to “find solace in the legacy of sacrifice, diligence and patriotism he left behind, especially in speaking up for the voiceless and underprivileged.”
Buhari prayed that God would accept his soul and comfort the family.