Marini's co-star Rachel Griffiths recently sparked speculation that the show would not be returning when she joked that she will soon be "unemployed".
ABC later denied the rumours and announced that no decision about the programme's future has been made yet, but Marini told Zap2It that the series should be renewed so that the storylines can be wrapped up.
"The thing is, Brothers & Sisters hasn't run its course," he said. "My ideal situation would be if ABC tells us it's the last season. Let's close it well. There's so many more storylines."
He continued: "ABC would be giving their respect to the audience and the 80 countries that watch this show. Close it well. It doesn't cost that much money. We're already in syndication. The show did well for the network. Hopefully, they give it another season and close it well."
Marini described Brothers & Sisters as a "strong" show and suggested that viewers "relate" to it.
"It's not every day you get a show like that with amazing actors," he said. "I'm not including myself in that - we're talking about Sally [Field], Rachel, Matthew Rhys and Calista [Flockhart]. People who have received awards and know what they're doing."
Brothers & Sisters airs on Sundays at 10/9c on ABC in the US and on Thursdays at 10pm on More4 in the UK.
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