Also on the bill were former Suede star Bernard Butler, 60s chart act Donovan - famed for tracks such as Hurdy Gurdy Man - and London Town hit-maker Ralph McTell.
Jansch, who was credited with influencing a generation of musicians, died in October 2011 at the age of 67 after a two-year battle with lung cancer.
The Scottish musician was a founding member of the group Pentangle, with whom he gave his last public performance in August of that year when they reformed.
Original members of the band - Terry Cox, Jacqui McShee and Danny Thompson, with Butler taking Jansch's place - were among those who joined the bill of last night's concert at the Royal Festival Hall on London's South Bank.
Jansch had been a prominent figure in the folk revival of the 1960s, and had been a recipient of a lifetime achievement honour at the BBC Folk Awards.
But his reputation as a virtuoso guitarist extended well beyond the folk circuit and he has often been cited as an influence by musicians such as Butler, who performed on his Crimson Moon album along with former Smiths star Johnny Marr.
Donovan said: "His impact is immense, it's extraordinary. The way he wrote song from blues into trad into jazz."
Plant - accompanied by Butler - performed Go Your Way My Love and then joined Bonnie Dobson to play Morning Dew at the concert, which was staged to celebrate Jansch's 70th birthday, which would have been a month ago.
The concert also included a specially recorded film from Neil Young, who performed Jansch's Needle Of Death from a recording booth at the home of US musician Jack White.