Ludlam has been rewarded for his fine club form, having been a stand-out player for Saints throughout the current campaign.
George Furbank did not make the matchday 23, while Courtney Lawes continues to go through head injury protocols and Tommy Freeman is out with hamstring injury.
Saracens lock Nick Isiekwe, who spent last season on loan at Saints, starts alongside Maro Itoje in the second row against Scotland this weekend.
Saints centre Rory Hutchinson has not made the Scotland 23.
Scotland team to face England: Hogg (c); Graham, Harris, Johnson, van der Merwe; Russell, Price; Sutherland, Turner; Z Fagerson; Gray, Gilchrist; Ritchie, Watson, M Fagerson.
Replacements: McInally, Schoeman, Nel, Skinner, Bradbury, White, Kinghorn, Tuipulotu.
England team to face Scotland: Steward; Malins, Daly, Slade, Marchant; Smith, Youngs; Genge, Cowan-Dickie, Sinckler; Itoje, Isiekwe; Ludlam, Curry (c), Simmonds.
Replacements: George, Marler, Stuart, Ewels, Dombrant, Randall, Ford, Nowell.
Ireland v Wales (Aviva Stadium, Dublin, 2.15pm)
Dan Biggar will skipper Wales against Ireland in the Six Natiions curtain-raiser at the Aviva Stadium on Saturday afternoon.
The Saints fly-half was named as captain for his country ahead of the tournament, and he will look to help Wales get off to a winning start in Dublin.
Wales team to face Ireland: L Williams; McNicholl, Adams, Tompkins, Rees-Zammit; Biggar (c), T Williams; Jones, Elias, Francis; Rowlands, Beard; Jenkins, Basham, Wainwright.
Replacements: Lake, Thomas, Lewis, S Davies, Moriarty, G Davies, Sheedy, Watkin.
Scotland Under-20s v England Under-20s (The Dam Health Stadium, Edinburgh, 8pm)
Three Saints players have been named in England Under-20s' starting line-up for the U20 Six Nations opener against Scotland Under-20s on Friday night.
Lock Tom Lockett and centres Ethan Grayson and Tom Litchfield are all in the first 15, selected by England head coach Alan Dickens, formerly of Saints.
There is another member of the Northampton squad among the replacements as full-back George Hendy gets set for a taste of the international action.
England Under-20s team to face Scotland Under-20s: Arundell; Bailey, Litchfield, Grayson, Dawkins; Johnson, Carr-Smith; Dormer, Stewart, Summerfield; Bell, Lockett; Wardell, Cripps, Knight (c).
Replacements: Spandler, Hobson, Hardwick, Rice, Fisilau, Jones, Benson, Hendy.