The seemingly random pals were spotted lounging on the shore, while Hudson, 35, wore a printed bikini and Martin, 38, wore a surfing wetsuit.
The Coldplay frontman caught some waves as the Barely Famous actress watched from the beach. Hudson's sons Ryder and Bing played with Martin's daughter Apple and son Moses and the group of six even went out to dinner together afterwards.
There was no indication as to whether the outing was romantic. Martin was last reported to have been in an on-again relationship with Oscar winner Jennifer Lawrence after Paltrow, 42, announced their decision to "consciously uncouple" last March after 10 years of marriage.
Hudson split from fiance Matt Bellamy in December 2014, and had a brief fling with Dancing With the Stars dance pro Derek Hough. Hudson and Paltrow are longtime friends.
"I look up to Gwyneth and how she has been in her life," Hudson told Harper's Bazaar in 2012. "She's the real deal."