"Yes, justice has been delayed but delivered finally. Nobody is above law and anyone who is involved in such a heinous crime should be brought to justice," the Congress MP told reporters outside Parliament.
He also said Congress leader Kamal Nath's name never figured in the list of those involved in the riots.
The riots, in which thousands of Sikhs were killed, broke out after the assassination of prime minister Indira Gandhi by her Sikh bodyguards on October 31, 1984.
Delhi Chief Minister Arvind Kejriwal welcomed the verdict convicting the 73-year-old Congress leader's conviction.
"It has been a very long and painful wait for innocent victims who were murdered by those in power. Nobody involved in any riot should be allowed to escape no matter how powerful the individual maybe," Kejriwal said on Twitter.
His AAP colleague and Supreme Court lawyer H S Phoolka also welcomed the judgement and thanked everyone for their support and help.
BJP spokesperson Tejinder Pal Singh Bagga, who is sitting on a hunger strike to Nath being named chief minister of Madhya Pradesh, said they will appeal in the apex court for death sentence to Kumar.
Nath is scheduled to be sworn in as chief minister in Bhopal later in the day.
A bench of Justices S Muralidhar and Vinod Goel convicted Kumar for criminal conspiracy, promoting enmity and acts against communal harmony.
The high court said Kumar's life imprisonment will be for the remainder of his life and asked him to surrender by December 31. It also asked him not to leave Delhi before that.