Nabi, 20, came through the West Bromwich Albion academy before leaving last summer and then had a spell with Indian Super League club Delhi Dynamos.
He has agreed a deal for the rest of the season, while Tomlinson, 27,  has arrived on non-contract terms after leaving Barnet in January after two years with the League Two club.
Keith Curle's Carlisle are sixth in League Two with eight games remaining.
As well as playing for Delhi, attacking midfielder Nabi also gained experience with Premier League side West Brom's Under-23s.
"Samir's had an excellent grounding and he's another who has something slightly different to what we already have in the group," Curle said.
Tomlinson has trained with the Cumbrians over the last week and has impressed former England international Curle.
"He has good habits and dynamics and he likes scoring goals and causing opposition defences as many problems as possible," he said.
"He's integrated quickly and well and he's shown us he has a good physical presence."
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Carlisle United have signed midfielder Samir Nabi and striker Ben Tomlinson.