Ed Sheeran Performs for Jury Deciding If 'Thinking Out Loud' Rips Off Marvin Gaye

Imagine if jury duty always included a live performance from Ed Sheeran -- that's what jurors got during his trial for allegedly ripping off Marvin Gaye's classic, "Let's Get It On."

Ed took the stand Thursday in a Manhattan federal courtroom, and at one point had his guitar with him to show the jury exactly how he writes songs, in general, and in particular ... his 2014 smash hit, "Thinking Out Loud."

He strummed the song's chords and sang the opening line ... "When your legs don't work like they used to before," and then testified he and co-writer Amy Wadge had nothing like Marvin's sexy times tune in mind when they wrote 'Thinking Out Loud.' Instead, he said their song was about maintaining love into old age.

He also explained, "When I write vocal melodies, it’s like phonetics." For instance, he says he first sang the song's hook as, "I'm singing out now" ... before it later became, "I'm thinking out loud."

The fact Sheeran was allowed to sit on the stand and give a live, although brief, performance could go a long way in swaying the jury. They're only human, so there's always potential for a "star-struck" factor -- and, sadly, Marvin Gaye isn't alive to sing in support of the plaintiffs.

As we reported, the estate of Ed Townsend -- co-writer of "Let's Get It On" -- is suing Sheeran, claiming his song copies the melody, harmony and other elements of Marvin's 1973 #1 hit.

During his testimony, Sheeran admitted he doesn't pour a heck of a lot of time into writing any of his songs ... saying he draws inspiration from whatever's happening in his life, and rarely takes more than one day to complete a song.