The 29-year-old shared the announcement on Twitter on 15 January.
"News just in... The new addition to the Shaw clan will be arriving summer time and @SirTomShaw and I are thrilled! #doubletrouble," she wrote.
Lane and her husband Tom Shaw are already parents to one-year-old Arthur.
The actress' husband tweeted: "Breaking news from the missus @lane_paula".
He later wrote: "Thank you to all who sent us such lovely messages. I'd like to buy you all a cyber pint. Cheers."
Thank you to all who sent us such lovely messages. I'd like to buy you all a cyber pint 🍺 Cheers— Tom Shaw (@SirTomShaw) January 16, 2016
The couple's pregnancy announcement comes just two weeks after they celebrated Arthur's first birthday.
In September 2015, Lane - who took three months' maternity leave after the birth of her first child - opened up about her first year in motherhood.
She told OK! Magazine: "I’ve not had sleepless nights, I’ve been very lucky. He’s a very good baby and very content.
"It’s a whole new ball game, but I love the chaos!"